A car bomb attack killed two US soldiers in Afghanistan on Thursday, at the same time that President Hamid Karzai was being sworn in for a second five-year term in the capital, NATO said.
The blast, which an Aghan army soldier called a suicide car bomb, occurred at 11:00 am (0630 GMT), as Karzai's inauguration ceremony got underway.
"Two US service members were killed in an improvised explosive explosion in Zabul province. It was a car bomb," Lieutenant Nicol Melendez told AFP.
"It was a suicide car bomb," an Afghan officer told AFP from the scene.
He said the bomber drove his explosives-packed car into the gate of a small US-run military base in the town of Qalat, the capital of Zabul province.
Suicide car bombings have become almost commonplace in Afghanistan as a Taliban-led insurgency gathers pace and the death toll of Western troops hits record levels.
The independent icasualties.org website puts the number of foreign military deaths so far this year at 473, compared to 295 for all of last year. Of those deaths, 290 are Americans.
Karzai pledged in his inauguration speech that Afghanistan wanted to take responsibility for its own security during the five years of his new term.
US President Barack Obama is considering requests from his commanders on the ground in Afghanistan to boost troop numbers by up to 40,000 and has said his decision will be revealed within weeks.
The new battle strategy being mulled by Obama includes switching emphasis from battleground fighting to training and mentoring Afghanistan's security forces to take over the battle against the Taliban.
Fundamental to this strategy is the notion that the sooner Afghanistan can take on its own fight, the sooner foreign forces -- 100,000 of whom fight under US and NATO command -- can drawdown for an eventual exit.