An Afghan security official told the BBC the bomber blew up a minibus he was driving when he was stopped by police on a road linking Kandahar to Herat.

The bus exploded near Afghan police and Canadian troops, killing three police and two civilians, and injuring others.

Taleban rebels have stepped up attacks on Afghan and foreign troops in 2008.

There were conflicting accounts of the circumstances surrounding the bombing, but a senior Afghan security official in Kandahar province told the BBC that police were following the minibus and signalled for it to stop.

"As soon as our police forces started searching, the attacker blew himself up," he said, describing the attack as "the work of the enemies of peace and stability".

Reports said four police were also injured in the attack, which took place on a road regularly targeted by the Taleban.

Afghan police are regularly targeted and killed by rebels.

According to Afghanistan's interior ministry, more than 700 police officers were killed in the first six months of 2008.

The majority of the casualties died in suicide attacks and roadside bombings.