Kandahar has seen a spate of violent incidents since the killing last week of Hamid Karzai's brother [EPA]

A gun battle between Afghan police and anti-government fighters in the city of Kandahar has killed up to four police officers, including a district police chief, according to government and hospital officials.

The incident on Wednesday morning came as a security handover designed to showcase the strength of Afghan forces took place in Lashkar Gar, the capital of neighbouring Helmand province.

The transition process, which will be accompanied by a gradual withdrawal of international forces, aims to put Afghan security forces in control of the whole country by the end of 2014.

Siddiq Siddiqi, a spokesman for the Afghan interior ministry, said the fighting in Kandahar was sparked by a police operation following a tip-off about the presence of two anti-government fighters hiding in a house in the area, including one he said was a senior Taliban commander.

The commander and one other fighter were killed along with three Afghan police in the raid, said the spokesman.

"Our police had intelligence about the presence of some terrorists in a house in District 1. Police besieged the house and ordered the terrorists to surrender, but they refused and started fighting," he said.

"In the fighting both terrorists including a well-known deaf Taliban commander known as Mullah Kar were killed."

But a doctor at Kandahar's Mirwais hospital said four policemen had been killed and three others wounded.

Bicycle bomber

Also on Wednesday, a blast triggered by a bicycle bomber in the northern city of Mazar-e Sharif killed four people and injured 12 others, according to security forces.

"We are investigating whether the explosive was attached to his body or his bicycle," said Sherjan Durani, a spokesman for the police chief of northern Balkh province.

In Lashkar Gar, Al Jazeera's Bernard Smith said the security transfer was going smoothly.

"It is a symbolic affair where we see Afghan forces officially take over responsibility for that part of Afghanistan," he said.

"This transition has been going on for quite sometime and the Afghan forces - the police and the military - have been taking the lead in patrolling and securing those areas.

"There will still be foreign forces, of course, but they will be in the background and they will be mentoring and giving guidance to Afghan forces as and when they ask for it." 

Security in Afganistan is under scrutiny after the recent killings of Ahmed Wali Karzai, Afghan President Hamid Karzai's half brother and one of the most powerful men in the country, and Jan Mohammad Khan, a senior aide to the president.

Western countries, which invaded Afghanistan in 2001 after the September 11 2001 attacks in the US, have begun to announce partial troop reductions starting this summer, with all 33,000 US "surge" troops due to leave by the end of 2012.

Around 150,000 foreign troops are stationed in Afghanistan, nearly 100,000 of whom are from the US.

Western officials say pulling troops from seven areas, which include the cities of Mazar-i-Sharif in the north, Herat in the west, and Lashkar Gah in the south, could take up to two years to implement.

Taliban says phones hacked

The Taliban, meanwhile, has denied reports about the death of their leader Mullah Mohammad Omar, saying false messages had been sent to media after their mobile phones, email accounts and a website were hacked into by US intelligence agents.
   
Mullah Omar, the Afghan Taliban's one-eyed, reclusive leader is among the most wanted men in the world, with a $10m US bounty on his head, and this is not the first time he has been reported dead.

"This is the work of American intelligence, and we will take revenge on the telephone network providers,"  Taliban spokesman Zabihullah Mujahid told the Reuters news agency.