NATO and Afghan forces have killed 25 Taliban fighters in assaults across southern Afghanistan, a government official and the defence ministry said Saturday, AFP reported.

In the deadliest incident, an air strike killed 20 militants late Friday in the Urgun district of Paktika province, said Hamidullah Zawak, spokesman for the provincial governor.

"As a result of the US-led coalition forces' air strike, 20 armed opposition were killed," he told AFP by telephone.

"These people intended to attack security posts and the US-led coalition. They were killed before they could do so."

The Afghan defence ministry said meanwhile five militants were killed in an Afghan army commando operation on Friday in the Gereshk district of Helmand province.

In Sangin district, also in Helmand, one Afghan soldier was killed and another injured during a small-arms attack, the ministry added.

Southern Afghanistan -- the spiritual heartland of the Taliban -- has seen the most fierce fighting since US-led international forces toppled the hardline Islamist regime in 2001.

US President Barack Obama is under pressure to order thousands more soldiers to Afghanistan, where the commander of the 100,000-strong US and NATO force, US General Stanley McChrystal, has reportedly asked for 40,000 extra troops.

NATO's commander in the south, Dutch Major General Mart de Kruit, told AFP in an interview this week that 10,000 to 15,000 more troops were required to ensure security in the region.

More Afghan soldiers and police, plus civilians to work in reconstruction and development projects, were also required, he said.