The blast was the latest to target Afghanistan`s security forces just a few months before US-led NATO troops start limited withdrawals after nearly 10 years of war against the Taliban.
"Insurgents have blown up an ambulance vehicle full of explosives which killed six members of the national security forces and wounded 10 more," including one civilian, the Kandahar governor`s office said.
The ambulance arrived after several insurgents armed with assault rifles and rocket-propelled grenades started firing on the police building.
It managed to pass through a security cordon and was detonated near where security forces were fighting the insurgents, said local police chief Khan Mohammad Mujahid.
The attack took place at a complex just outside Kandahar which is used for police training as well as army and police recruitment.
A new police headquarters for the city is also being built there, following a Taliban attack on the previous office in February which left 19 people dead.
Kandahar is the de facto capital of southern Afghanistan and the birthplace of the Taliban militia waging an insurgency against US-led troops. Local police and officials are frequently targeted.
The Taliban claimed responsibility for the assault, with spokesman Yousuf Ahmadi telling AFP that four of their fighters had entered the police centre.
The attack is the latest aimed at Afghanistan`s roughly 120,000-strong police, who will play a growing role in the country`s security as international troops start a limited withdrawal from seven relatively peaceful areas in July.
Last month, the police chief of the northern province of Kunduz was killed by a suicide bombing also claimed by the Taliban.
Around 130,000 NATO troops, about two-thirds of them from the United States, are in Afghanistan fighting the Taliban and other groups.
Their first limited withdrawals are due to start in July ahead of a planned transition to Afghan control of security across the country in 2014.
Elsewhere, the military said NATO troops hunted down an Afghan policeman who shot dead two American soldiers this week, killing him with the help of intelligence tip-offs.
Wearing a border police uniform, the man shot the soldiers inside a police compound on Monday while US military advisers were holding talks with a local colonel. The colonel later identified them as American.
The gunman fled, but was tracked down using "multiple intelligence reports" the NATO-led International Security Assistance Force (ISAF) said.
"The successful operation resulted in the death of the individual responsible for the shooting," it said.
In Kabul, demonstrations against the burning of a copy of the Koran by a US pastor, which have killed at least 24 people, including seven UN workers, entered a seventh day when several hundred people gathered outside a mosque.
Twelve people died in the protests in Kandahar on Saturday and Sunday.
NATO-led forces claim the Kandahar area, seen as strategically important due to its strong Taliban links and proximity to the Pakistani border, is safer following intense fighting in recent months despite recent attacks. (*)
Editor: Kunto Wibisono
Copyright © ANTARA 2011
