LASHKAR GAH, Afghanistan - Afghan, British and U.S. troops have launched a major offensive to retake the only sizeable town held by Taliban insurgents in Afghanistan, Afghan and foreign forces said on Saturday.

The town of Musa Qala in the southern province of Helmand has been the Taliban's biggest power base in Afghanistan since they seized it from tribal elders in February. British troops pulled out of the town a year ago in a truce that handed the elders control after coming under sustained Taliban attacks.

U.S. troops inserted close to the town by helicopter on Friday to begin the attack as British troops moved in by land.

"We are now involved in an advance that is effectively kicking the door in to Musa Qala," said Lieutenant Colonel Richard Eaton, British forces' spokesman in Helmand.

Afghan army units are preparing to follow up the assault on several hundred rebels in and around the town.

Fighting continued on Saturday, but there were no casualties among the NATO-led and U.S.-led coalition forces.

The NATO-led International Security Assistance Force (ISAF) does not release Taliban casualty figures, but the separate U.S.-led coalition force said an air strike had killed several Taliban including a militant commander in Musa Qala on Friday.

A Taliban commander in Musa Qala said the insurgents had destroyed two NATO armoured vehicles and killed many foreign troops, without suffering any casualties.

Thousands of Taliban fighters were fighting to defend the town, the commander, Mullah Qasam told Reuters by satellite telephone. The Taliban frequently exaggerate foreign casualties.

The Afghan Defence Ministry said the operation was launched following a request from local tribal chiefs.

U.S.-led and Afghan forces toppled the Taliban for refusing to give up al Qaeda leaders after the September 11, 2001 attacks on the United States.

But foreign forces had only a limited presence in Helmand allowing the Taliban to regroup and take control of large parts of the mainly desert province till around 7,000 British troops moved in some 18 months ago.

Since then, there has been fierce fighting as British-led ISAF troops, backed by Afghan forces have gradually wrested control of the major towns back from the Taliban.

But the Taliban still control parts of the fertile Helmand River valley that runs through the desert and have launched hit-and-run attacks and suicide bombs elsewhere to destabilise the province and weaken government control.

The Taliban relaunched their insurgency two years ago with guerrilla attacks in the south and east and suicide bombings on cities across the country aimed at convincing Afghans their government and its Western allies cannot bring security.

In a separate incident, a district chief and six of his bodyguards were killed in an ambush on a road in Farah province bordering Helmand on Saturday, a provincial official said.

An Afghan military commander and five of his body guards were killed in a similar incident on Friday in the western province of Herat, but it was not clear who carried out that attack.