The fighting in southern Helmand province's Musa Qala district at dawn Sunday was the heaviest since September, when local tribal chiefs had agreed to push the Taliban out of the area.

Some "70 to 80 insurgents were killed" after they attacked a Nato-led International Security Assistance Force (Isaf) patrol in the area, Isaf spokesman Major Luke Knittig told AFP.

The toll was an estimated number reported by military commanders in the fighting zone, located between Musa Qala and neighbouring Nawzad district, Knittig said.

He said Nato warplanes were also called in to support ground troops.

"It's an estimation. The ground commanders reported through reports from troops engaging the enemy," he said.

Afghan authorities earlier said four Taliban fighters were killed in fighting involving Isaf and Afghan security forces. It was not immediately clear if they were referring to the same battle.

Musa Qala saw some of the worst Taliban battles with Afghan and Nato-led troops this year until September, when tribal chiefs agreed to not allow the Taliban in their region.

In return, British troops operating under Isaf pulled their troops from the area.

Knittig said the fighting at the weekend took place outside the troubled district.

"Geographically this engagement took place between Nawzad and Musa Qala," he said, referring to a neighbouring district also hit by Taliban violence.

This year has been the bloodiest since the fall of the Taliban in late 2001 after a US-led invasion, with more than 100 suicide bombings killing 230 Afghans and 17 foreign troops, according to Isaf figures.

More than 3,700 people -- including a majority of insurgents as well as about 1,000 civilians, plus Afghan soldiers and police -- have been killed this year, four times the toll for 2005, according to an official report.