A suicide attacker in police uniform blew himself up inside a provincial police headquarters in Afghanistan on Monday, killing two foreign soldiers and two Afghans, police said.

A spokesperson for the Taliban insurgent movement, Zabihullah Mujahed, said his group had carried out the attack in the normally calm northern province of Baghlan as foreign soldiers were training Afghan police.

US Forces Afghanistan confirmed that two "service members" from the US-led coalition were killed and three were wounded in the suicide attack.

The incident was being investigated and the nationalities of the casualties could not be released, it said in a statement.

Afghan police said the troops involved were US nationals.

"At 9:30 am today a suicide attacker in police uniform got into the police headquarters of the province," spokesperson Ahmad Jawid Basharat told AFP.

"He entered the criminal investigation department where American soldiers from NATO were advising the Afghan police. They often come here to do this."

"He detonated and killed two American soldiers and one Afghan policeman. One American soldier and three police were wounded. A child who was outside the building was also killed," Basharat said.

Provincial governor Abdul Jabar Haqbine earlier told AFP that one foreign soldier and a child, the son of a cleaner, had died in the attack.

There are about 33 000 US troops in Afghanistan in the NATO-led International Security Assistance Force and a separate US-led coalition.

They, and roughly the same number of soldiers from nearly 40 other countries, are working to fight a Taliban-led insurgency as well as train Afghan security forces.

Baghlan sees little of the Taliban-led violence plaguing Afghanistan, which has been hit by a wave of suicide bombings in the past three years.

However, around 80 people were killed in a suicide bombing in the province in November last year that struck a party of parliamentarians visiting a sugar factory.

Six MPs were among the dead as were scores of school children.

At the time it was the worst suicide attack in Afghanistan since the country became caught up in an insurgency led by the Taliban, who were in government between 1996 and 2001.

It was eclipsed by a suicide attack in the southern city of Kandahar in February that killed about 100 people. Also on Monday, a coalition helicopter was brought down by a "enemy fire" in the province of Wardak, adjoining Kabul, but the 10 crew were all evacuated safely, US Forces Afghanistan said in a separate statement.

"The helicopter crew was exchanging fire with the enemy prior to sustaining damage," it said.

And police said eight Afghan employees of a private road construction company were killed in international air strikes aimed at insurgents in central Afghanistan at the weekend.

The US-led coalition said it was investigating the claims, which surfaced on Sunday when local media reports said up to 23 guards of a private road construction company were killed in the strikes in Ghazni.

Afghan authorities meanwhile accused Taliban insurgents of kidnapping 14 Afghan road construction workers in the eastern province of Kunar on Sunday.

And the interior ministry said an Afghan guard who shot dead a South African and a Briton in the capital on Saturday may have planned a "terror attack" although he had also intensely disliked the men.

South African Jason Breseler and Briton David Giles — respectively the head and deputy head of international shipping group DHL in Afghanistan — were shot dead in their vehicle Saturday as they pulled up outside their offices.

The guard who shot them then turned the gun on himself.

AFP