KABUL: A bomb blast in Afghanistan's restive south killed two NATO soldiers, hours after the death of an American trooper in a separate attack, a statement said Saturday.

"Two ISAF service members were killed in southern Afghanistan as a result of an IED strike yesterday," said a statement from NATO's International Security Assistance Force, referring to an improvised explosive device.

ISAF did not give their nationalities.

IEDs, along with suicide bomb attacks, are the main weapons deployed by Taliban militants, and have become more powerful and deadly as foreign forces enhance security procedures, military officials have said.

The bombs, made principally from fertiliser and detonated by remote control, can range up to 2,000 pounds (900 kilograms), a senior US military intelligence official said recently, destroying even the heaviest armoured vehicles.

The southern provinces of Helmand and Kandahar are the most violent, but the Taliban has spread its fight to previously peaceful regions.

Foreign troops under US and NATO command currently number around 113,000 and are being reinforced with another 40,000 over the course of this year as the counterinsurgency strategy moves into high gear.

Five soldiers -- four American and one French -- died on Wednesday. On Monday, three US, two French and a British soldier were killed in violence in the deadliest day for international troops since October.