Anti-government protesters have rejected Saleh's offer to step down by the end of the year [EPA]

Presidential guards loyal to Ali Abdullah Saleh, the Yemeni president, have clashed with army units who have backed opposition groups and protesters demanding Saleh's resignation.

The clashes took place in the town of Mukalla, in the eastern Hadramout province, on Thursday.

A colonel was wounded, but it was not clear whether he was on the side of the elite Republican guard, which is loyal to Saleh, or the regular army, a local government source told the Reuters news agency.

General Ali Mohsen, commander of the country's northwestern zone and widely seen as the country's second-most powerful figure, said earlier this week that he was supporting pro-democracy protesters who have been demonstrating for weeks, calling for Saleh to leave office after three decades in power.

A similar clash took place in the same town earlier this week, leaving one dead on either side.

The Civil Bloc, an umbrella group of civil society organisations, has called for a "transitional council" of nine figures "not involved with the corruption of the old regime" to draw up a new constitution ahead of elections to be held in six months.

Opposition parties had earlier rejected Saleh's offer to step down from power by January 2012, rather than September 2013 when his current term ends.

In yet another blow to the president, Sheikh Sinan Abu Lohoum, the head of the Baqeel tribe, which is Yemen's largest, also announced his support for the opposition on Thursday.

Speaking to Al Jazeera, Abdul Ghani al-Iryani, a political analyst, warned that the risk of "civil war" is heightened by clashes between the army and the presidential guard, which is commanded by Saleh's son, Ahmed.

"With the military divided, the risk of confrontation and escalation is just too great. Right now it's at a very low level, and it won't start an all-out battle, but the risk is still there."

Al-Iryani termed Saleh's offer to step down at the end of this year as "too little, too late".

"This was on the table some time ago, and the president rejected it," he said.

"Right now, it is unworkable, because the military is divided, and the tanks are facing off in the streets and we cannot afford ... to have this kind of tension that could turn into civil war at any moment, just to maintain the pride of one man.

"He does not seem to realise how precarious his position is, and he continues to make offers that are way too little for the balance of power that now exists on the ground. The people are up against him, half the military is against him, the international community is against him and he needs to understand that he has to leave quickly."

Al-Iryani told Al Jazeera that Saudi Arabia, the Gulf Cooperation Council countries and western powers were currently working to "facilitate some kind of peaceful transition" of power.

Protesters who have camped in Sanaa's university square in their thousands for the last six weeks have hardened their stance against the president, and say they are planning a "Day of Departure" for this Friday.

Ten thousand protesters gathered in the square again on Thursday, calling for Saleh to leave office.

'Weapons smuggling' bid foiled

Meanwhile, police in Dubai say they have foiled an attempt to smuggle 16,000 pistols into Yemen from Turkey.

Dahi Khalfan Tamim, Dubai's police chief, said in a statement on Thursday that his forces had intercepted the Turkish-made pistols, said to be worth $4.36 million.

Tamim said five Arab residents of the United Arab Emirates and one Turkish man were arrested in the operation. The consignment landed in Dubai by ship, for transit to Saada, in northern Yemen.

Dubai police say the weapons were hidden in a cargo shipping container, and were discovered in a Dubai warehouse two weeks ago. The weapons were said to be hidden behind boxes of furniture wrapped in plastic.

Police say the shipment passed through an Egyptian port before arriving at the Gulf emirate.

Tamim also showed photographs of the shipment, which is the largest arms bust in the Emirates' history.

It remains unclear who the intended recepients of the weapons were, but Tamim said they were "definitely not [going] to the government".

Yemen, which sits on a major shipping lane and borders oil giant Saudi Arabia, is the second most heavily armed country in the world in per capita terms. Around half its 23 million people own a gun.

UK urges Yemen exit

The United Kingdom has all but closed its embassy in Yemen, and has urged its citizens to leave the country as soon as possible in order to avoid being caught up in the country's deepening unrest.

The country's foreign office said on Wednesday that it was leaving only a skeleton staff at its embassy in Sanaa, and called on any Britons still in the country to "leave now", as the government may not be in a position to offer them consular assistance if the situation worsens.

Yemen has seen increasingly bloody violence, as the embattled Saleh clings to power amid a wave of revolt. Saleh on Wednesday took on emergency powers, suspending the constitution, barring protests and giving far-reaching powers to his security forces.

The political opposition has joined with protesters in their demand for Saleh to leave office, and there is a likelihood of further violence in the country, which has already seen dozens of demonstrators killed in clashes with authorities.