Kabul: US-led coalition and Afghan troops killed more than 220 suspected Taliban militants in an operation in southern Afghanistan last week, the US military said on Monday, the biggest recent toll of insurgent deaths.

Residents said that more than 70 civilians were killed in air strikes by foreign forces in the Sangin district of Helmand province.

"The operation is mostly wrapped up. The troops killed more than 220 militants," US military spokes-man Nathan Perry said. He was not aware of any civilian casualties.

Violence in Afghanistan has surged this year to its worst level, the bloodiest period since the Taliban's ouster in 2001, and tempers have been running high over rising civilian casualties.

The four-day operation in Helmand was launched after militants attacked a military convoy carrying equipment for a power-supply dam in the Kajaki area.

"Afghan National Security Forces and coalition forces were attacked repeatedly with small arms and heavy-weapons fire during multiple engagements," the US military said in a statement.

"The soldiers responded with small-arms fire, heavy-weapons and close air support, eliminating the militant threats."

There were no military casualties in the fighting in the area between Sangin and Kajaki districts, Perry said.