KABUL: Afghan and US-led coalition troops killed 35 militants in clashes and air strikes in southern Afghanistan, the military said Friday, announcing the latest in a series of heavy battles.

The fighting erupted early Thursday when troops came under heavy fire while on patrol in the southern province of Zabul, the US military said.

"The combined forces returned fire and requested air support, killing 35 and wounding 13," it said in a statement.

The remaining militants retreated and the wounded were treated and taken into Afghan army custody, it said.

No troops or civilians were reported hurt, the statement said.

The military did not say whether the militants were suspected Taliban but fighters from that group operate in Zabul and other provinces in the south.

It was impossible independently to confirm details of the clash in Zabul's Daychopan district.

The battle came as heavy fighting erupted further east, closer to the Pakistan border, when Afghan and foreign security forces raided an encampment where they said fighters in the Haqqani Taliban network were gathered.

The Afghan defence ministry said 35 militants were killed in that clash early Thursday. Six blew themselves up to avoid capture, it said.

The US military said around 30 died.

Fighting linked to a Taliban-led insurgency has picked up in recent weeks, with insurgents stepping up bomb attacks and security forces hitting back with major operations.