Soldiers under heavy attack in southern Afghanistan called in air support during hours of fighting that left several dozen militants dead and two foreign troops hurt, the US-led coalition said yesterday.

The Helmand attack took place 17 kilometres (10 miles) from the centre of the district of Sangin, which Taliban fighters held for weeks before it was retaken by the government and its foreign allies in April.

"As the battle raged on into the night, additional enemy fighters arrived from the west side of the Helmand River to reinforce several enemy positions in a trench line," a coalition statement said.

Coalition helicopters and war planes dropped bombs on rebel positions.

"The prolonged battle killed several dozen enemy combatants," the statement said.

Two coalition soldiers were hurt. The statement did not give the nationalities of the wounded troopers.

The strike came hours after the deadliest insurgent attack since the Taliban fell in 2001.

Police said Monday they had detained a suspect in connection with the deadly suicide bombing that destroyed a bus full of police instructors at Kabul's busiest transportation hub, killing 35 people and wounding 52.

In an operation backed by Afghan troops, jets on Sunday targeted a compound that also contained a mosque and a madrasa, or Islamic school, in the Zarghun Shah district of Paktika province. Early reports indicated seven children at the madrasa and "several militants" were killed, and two militants detained, the statement said.

Meanwhile, police detained a suspect in the Kabul bus bombing after he was caught filming the aftermath of the deadly suicide blast, said Ali Shah Paktiawal, Kabul police director of criminal investigation.

The suspect, whose name and nationality were not disclosed, had pictures of the slain Taliban leader Mullah Dadullah in his phone, as well as text messages from a foreign country, Paktiawal said.

Sunday's enormous blast, which raised the spectre of an increase in Iraq-style bombings with heavy casualties, was at least the fourth attack against a bus carrying Afghan police or army soldiers in Kabul in the last year. The bomb sheared off the bus' metal sidings and roof, leaving a charred frame.