|Kandahar has been hit by a series of violent incidents since the killing last week of President Karzai's half-brother [EPA]
A gun battle between Afghan police and anti-government fighters in the southern city of Kandahar has killed up to four police officers, including a district police chief, according to government and hospital officials.
Sediq Seddiqi, a spokesman for the Afghan interior ministry, said Wednesday's clash was sparked by a police operation following a tip-off about the presence of two anti-government fighters - including an alleged senior Taliban commander - hiding in a house in the area.
The commander and one other fighter were killed along with three Afghan police officers in the raid, Seddiqi said.
"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.
In the day's second deadly incident, a blast triggered by a bicycle bomber in Mazar-e-Sharif, in the northern Balkh province, 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," Sherjan Durani, a spokesman for the provincial police chief, said.
Wednesday's violence coincided with a security handover in Lashkar Gah, the capital of the southern Helmand province, designed to demonstrate the strength of Afghan forces.
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.
Al Jazeera's Bernard Smith, reporting from Lashkar Gah, said the transfer was proceeding smoothly in Lashkar Gah.
"It is a symbolic affair where we see Afghan forces officially take over responsibility for that part of Afghanistan," he said.
|Simon Gass, NATO's senior civilian representative in Afghanistan, discusses the security transition
"This transition has been going on for quite some time 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, 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 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 Mazar-i-Sharif, Lashkar Gah and the western city of Herat, could take up to two years to implement.
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 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," Zabiullah Mujahid, the Taliban spokesman, told the Reuters news agency.