23 January 2015 Last updated at 04:36 ET

Yemen profile

A chronology of key events:

1500s - Ottomans absorb part of Yemen into their empire but are expelled in the 1600s.

1839 - Aden comes under British rule, and when the Suez Canal opens in 1869 serves as a major refuelling port.

1849 - Ottomans return to north, but later face revolt.

1918 - Ottoman empire dissolves, North Yemen gains independence and is ruled by Imam Yahya.

1948 - Yahya assassinated, but his son Ahmad beats off opponents of feudal rule and succeeds his father.

1962 - Imam Ahmad dies, succeeded by his son but army officers seize power, set up the Yemen Arab Republic (YAR), sparking civil war between royalists supported by Saudi Arabia and republicans backed by Egypt.

South Yemen formed

1967 - Formation of southern Yemen, comprising Aden and former Protectorate of South Arabia. Country is later officially known as the People's Democratic Republic of Yemen (PDRY). Programme of nationalisation begins.

1971 - Thousands flee to north following crackdown on dissidents. Armed groups formed in bid to overthrow government.

1972 - Border clashes between YAR and PDRY, ceasefire brokered by Arab League.

1978 - Ali Abdallah Saleh named as president of YAR.

1979 - Fresh fighting between YAR and PDRY. Renewed efforts to unite the two states.

1982 - Earth quake kills 3,000.

1986 - Thousands die in south in political rivalry. President Ali Nasser Muhammad flees the country and is later sentenced to death for treason. New government formed.

North and south unite

1990 May - Unified Republic of Yemen proclaimed, with Saleh as president.

1991 - Yemen opposes US-led action against Iraq in Gulf War.

1992 - Food price riots in major towns.

1993 April - Coalition government formed, made up of ruling parties of former north and south.

1993 August - Vice-President Ali Salim al-Baid withdraws to Aden, alleging that south is being marginalised and that southerners are being attacked by northerners.

1994 - Armies of former north and south, which have failed to integrate, gather on former frontier as relations between southern and northern leaders deteriorate.

Attempted split

1994 May - Saleh declares state of emergency and dismisses al-Baid and other southern government members following political deadlock and sporadic fighting. Foreigners flee escalating fighting.

1994 May 21- Al-Baid declares independence of Democratic Republic of Yemen. Saleh rejects secession as illegal.

1994 July - Northern forces take control of Aden, secessionist leaders flee abroad and are sentenced to death in absentia.

1995 - Yemen, Eritrea clash over disputed island territory.

US vessel attack

2000 October - US naval vessel USS Cole damaged in suicide attack in Aden which is subsequently blamed on al-Qaeda. Seventeen US personnel killed.

2000 October - Bomb explodes at British embassy. Four Yemenis who are jailed say they carried out attack in solidarity with Palestinians.

2001 February - Violence in run-up to municipal polls and referendum, in which voters show support for constitutional reform extending presidential term and powers.

Terror crackdown

2001 November - President Saleh visits US, tells President Bush that Yemen is a partner in the fight against terrorism.

2002 February - Yemen expels more than 100 foreign Islamic scholars, including British and French nationals, in crackdown on terror and suspected al-Qaeda members.

2002 October - Supertanker Limburg badly damaged in attack, blamed on al-Qaeda, off Yemeni coast.

2003 April - The 10 chief suspects in the bombing of the USS Cole escape from custody in Aden.

2004 March - Two militants, suspected of masterminding bombing of USS Cole, are re-arrested.

Clashes in north

2004 June-August - Government troops battle supporters of dissident cleric Hussein al-Houthi in the north; estimates of the dead range from 80 to more than 600.

2004 August - Court sentences 15 men on terror charges, including bombing of Limburg tanker in 2002.

2004 September - Government says its forces have killed dissident cleric Hussein al-Houthi, the leader of a revolt in the north.

2005 March-April - More than 200 people are killed in a resurgence of fighting between government forces and supporters of the slain rebel cleric Hussein al-Houthi.

2005 May - President Saleh says the leader of the rebellion in the north has agreed to renounce the campaign in return for a pardon. Minor clashes continue.

2005 July - Police and witnesses say at least 36 people are killed across the country in clashes between police and demonstrators protesting about a cut in fuel subsidies.

2005 December - More than 60 people are killed when a landslide destroys a mountain village around 20km from Sanaa.

2006 March - More than 600 followers of slain Shia cleric Hussein al-Houthi who were captured following a rebellion he led in 2004 are released under an amnesty.

2006 September - President Saleh wins another term in elections.

2007 January-March - Scores are killed or wounded in clashes between security forces and al-Houthi rebels in the north.

2007 June - Rebel leader Abdul-Malik al-Houthi accepts a ceasefire.

2007 July - Suicide bomber attacks a tourist convoy killing eight Spaniards and two Yemenis in the province of Marib.

2007 August - Citizens banned from carrying firearms in Sanaa. Demonstrations without a permit are outlawed.

2007 October - Volcano erupts on the Red Sea island of Jabal al-Tair where Yemen has a military base.

2007 November - Clashes between Yemeni tribesmen and army personnel protecting a Ukrainian oil company leave 16 people dead in the south-eastern Shabwa province.

2008 January - Renewed clashes between security forces and rebels loyal to Abdul-Malik al-Houthi.

2008 April - Clashes with troops as southern Yemenis protest against alleged northern bias in state job allocation. One man killed.

2008 March-April - Series of bomb attacks on police, official, diplomatic, foreign business and tourism targets. US embassy evacuates all non-essential personnel.

2008 September - Attack on US embassy in Yemeni capital Sana'a kills 18 people, including six assailants. Six suspects arrested.

2008 October - President Saleh announces arrest of suspected Islamist militants allegedly linked to Israeli intelligence.

Demands for reform

2008 November - Police fire warning shots at Common Forum opposition rally in Sanaa. Demonstrators demand electoral reform and fresh polls. At least five protesters and two police officers injured.

2009 February - Government announces release of 176 al-Qaeda suspects on condition of good behaviour.

2009 June - Nine foreigners are abducted in remote Saada region. The bodies of three are later found. The fate of the remaining six hostages remains unclear, though local rebels deny responsibility.

2009 August - The Yemeni army launches a fresh offensive against Shia rebels in the northern Saada province. Tens of thousands of people are displaced by the fighting.

2009 October - Clashes break out between the northern rebels and Saudi security forces along the two countries' common border. The rebels accuse Saudi Arabia of supporting the Yemeni government in attacks against them. The Saudi government denies this.

2009 November - Saudi Arabia says it has regained control of territory seized by Yemeni rebels in a cross-border incursion.

2009 December - Yemen-based branch of al-Qaeda claims it was behind failed attack on US airliner. The government calls on the West for more support to help it combat the al-Qaeda threat.

2010 January - President Saleh says government open to talks with Al-Qaeda militants, provided they renounce violence.

2010 February - Government signs ceasefire with northern rebels.

2010 March - Northern rebels release 178 captives after the government accuses the Shia Houthi group of failing to comply with the terms of the truce reached in February.

2010 September - Thousands flee government offensive against separatists in southern Shabwa province.

2010 October - Global terror alert after packages containing explosives originating in Yemen are intercepted on cargo planes bound for the US.

2010 December - Yemen says 3,000 soldiers killed in recent outbreak of fighting involving Houthi rebels.

2011 January - US Secretary of State Hillary Clinton visits to express "urgent concern" at al-Qaeda activities in Yemen.

Tunisian street protests which unseat President Ben Ali appear to encourage similar demonstrations in other countries, including Yemen.

President Saleh pledges not to extend his presidency in 2013 or to hand over to his son.

2011 March - Pro-reform demonstrations continue. Police snipers open fire on pro-democracy camp in Sanaa, killing more than 50 people.

Senior military figures including key general, Ali Mohsen al-Ahmar, declare their backing for protest movement. Several ministers and other senior regime figures also defect to protesters.

President Saleh says unrest risks plunging country into civil war. State of emergency is imposed.

2011 April - Unrest and violent government response continue. President Saleh vows to remain in office.

2011 May - Dozens die in clashes between troops and tribal fighters in Sanaa. Airport shuts and thousands flee the city.

2011 June - President Saleh is injured in a rocket attack and is flown to Saudi Arabia.

British and French forces prepare to evacuate foreigners in the event of a civil war.

2011 September - President Saleh returns home.

US-born al-Qaeda leader Anwar al-Awlaki is assassinated by US forces.

2011 October - Yemeni human rights activist Tawakul Karman wins Nobel Peace Prize, together with Ellen Johnson Sirleaf and Leymah Gbowee of Liberia.

UN Security Council passes resolution condemning violence, calls for transfer of power.

Unity government

2011 November - President Saleh agrees to hand over power to his deputy, Abdrabbuh Mansour Hadi.

Unity government - including a prime minister from the opposition - is formed.

2012 January - President Saleh leaves country. Parliament grants him full immunity in the face of objections from thousands of street protesters.

2012 February - Abdrabbuh Mansour Hadi inaugurated as president after uncontested elections.

2012 May - International donors pledge more than $4bn in aid to Yemen to help improve infrastructure and security. Aid agencies warn that Yemen is on the brink of food crisis. The government is thought to have asked for some $10bn.

An al-Qaeda leader Fahd al-Quso in Yemen wanted over the 2000 bombing of the US warship USS Cole is killed in an unmanned drone attack.

2012 June - The army recaptures three al-Qaeda strongholds in the south - Shuqra, Zinjibar and Jaar.

2012 September - Defence Minister Muhammad Nasir Ahmad survives car bomb attack in Sanaa that kills 11 people, a day after local al-Qaeda deputy head Said al-Shihri is reportedly dead in the south.

2012 November - A Saudi diplomat and his bodyguard are shot dead in Sanaa. Security officials say the assailants, who opened fire on the diplomat's convoy, were dressed in police uniforms.

National dialogue

2013 March - Delayed national dialogue conference begins with aim of drafting new constitution.

2013 April - Ahmed Ali Saleh, son of ex-president Saleh, is removed as head of Republican Guard.

2013 July - US intensifies drone strikes against al-Qaeda.

2013 August - Several foreign embassies shut temporarily over fears of attacks by al-Qaeda.

2013 December - The shooting of a tribal leader at a military checkpoint in the eastern province of Hadramawt sparks mass protests in the provincial capital Mukalla.

2014 January - National Dialogue Conference winds up after ten months of deliberation, agreeing a document on which the new constitution will be based.

2014 February - Presidential panel gives approval for Yemen to become a federation of six regions as part of its political transition.

2014 July - Tribesmen blow up the country's largest oil pipeline, disrupting supplies from the interior to a Red Sea export terminal.

2014 August - President Hadi sacks his cabinet and overturns a controversial fuel price rise following two weeks of anti-government protests in which Houthi rebels are heavily involved.

2014 September - Houthi rebels take control of the capital Sanaa. The UN brokers a peace deal according to which the Houthis agree to withdraw their fighters from cities they have seized once a new national unity government has been formed.

2015 January - The Houthis reject the draft of a new constitution proposed by the government. They seize state TV and clash with troops in the capital, in what the government called a coup attempt.

President Hadi and his government resign in protest at the takeover by Houthi rebels of the capital.