A bomb attack on Thursday killed five NATO troops in southern Afghanistan, the main battleground with the Taliban, the US-led International Security Assistance Force (ISAF) said.

"Five International Security Assistance Force service members died following an improvised explosive device attack in southern Afghanistan today," an ISAF statement said, without giving any further details in line with policy.

Single bomb attacks killing as many as five foreign soldiers are relatively infrequent in Afghanistan. An ISAF spokesman declined to give further details when questioned by AFP.

The deaths come a week after the Taliban shot down a US helicopter, killing 30 Americans in the biggest single loss of US life in the 10-year war.

At least 387 coalition soldiers have now been killed in Afghanistan so far this year, according to an AFP tally based on that kept by independent website icasualties.org.

That compares to a total of 711 deaths for the whole of last year.

Southern Afghanistan has seen the worst fighting since the 2001 US-led invasion brought down the Taliban regime, sparking an increasingly deadly insurgency against foreign troops and the Afghan government.

The area is the Taliban's heartland and was the focus of a US troop surge from 2010 which commanders say has made significant progress against the insurgents.

However, the Taliban still frequently target foreign forces with crudely-assembled improvised explosive devices (IEDs) which frequently strike troops on foot patrol or travelling in armoured vehicles.

From April to June of this year, 3,485 IEDs exploded or were found in Afghanistan, according to the Pentagon's Joint IED Defeat Organisation (JIEDDO) -- a 14 percent increase over the same period last year.