The U.S. military Friday was investigating whether an explosion at a weapons cache that killed seven American soldiers and wounded three was an accident or an attack.

Thursday's blast -- one of the deadliest for U.S. forces since they deployed here two years ago -- also left another American soldier missing and wounded an Afghan interpreter.

Afghan officials called it an accident, but Lt. Col. Bryan Hilferty, a spokesman at U.S. military headquarters in Kabul, said its investigators were still looking into the explosion.

The blast occurred as the soldiers worked around the cache of rifle ammunition and mortar rounds in the village of Dehe Hendu, about 90 miles southwest of the capital, Kabul, in Ghazni province.

Hilferty said nothing indicated "active enemy activity" at the site of the explosion, but said investigators were exploring the possibility that "it could have been a booby-trap."

He said it was unclear whether the soldiers were handling the weapons, which he said included rifle ammunition and mortar rounds. He gave no details of where the weapons were concealed.

Ghazni province Gov. Haji Asadullah Khan said the blast was set off by mistake as the soldiers were trying to defuse arms at an old weapons depot found in an open area.

"I'm sure it wasn't a plot by the Taliban," Khan said. "We know the area and the people are good."

The deaths come at the end of a bloody month that has underlined the danger and instability still plaguing Afghanistan two years after a U.S.-led invasion ousted the hard-line Islamic Taliban (search) regime for harboring Usama bin Laden (search) and the Al Qaeda (search) network.

Coalition soldiers regularly uncover and destroy caches of weapons, much of it dating back to the U.S.-backed mujahedeen resistance against the Soviet occupation in the 1980s. Residents often lead military units to the caches -- a sign, the military says, that it is winning the confidence of Afghans tired after almost a quarter-century of strife.

The wounded soldiers were evacuated to a hospital at Bagram Air Base, the main camp of the U.S.-led coalition in Afghanistan. Hilferty said the three soldiers and the interpreter were released after treatment.

Names of the victims were not released.

This month alone, about 80 people have died in violence in Afghanistan, including civilians, militants, police officers, international peacekeepers and American soldiers.

Only 16 U.S. soldiers died in the initial combat in Afghanistan in 2001, but the death toll earlier this month from all anti-terrorist missions worldwide under Operation Enduring Freedom reached 100 -- of those about two-thirds in Afghanistan, half in combat and the rest in accidents.

The United States provides 9,000 of the 11,000-member anti-terror coalition troops stationed in Afghanistan. Officials say U.S. forces are preparing a spring offensive against Taliban and Al Qaeda holdouts amid concern that operations in Afghanistan haven't been as effective in breaking up terrorist networks as they had hoped.

Hilferty said Thursday that the U.S. military is "sure" it will catch bin Laden -- chief suspect in the Sept. 11, 2001, attacks that sparked the U.S.-led invasion of Afghanistan -- this year, perhaps within months.

Separately, investigators also are sifting through evidence from homicide bombings that killed British and Canadian soldiers in Kabul earlier this week. The Taliban has claimed responsibility for both blasts, alleging they are the start of a bombing campaign across the country.

British troops held a memorial Thursday for Pvt. Jonathan Kitulagoda, 23, of Plymouth in southwest England, killed the day before by a homicide bomber.

Kitulagoda was killed when a homicide bomber detonated a taxi next to an unarmored jeep. Four other British soldiers were wounded. That attack came a day after a Canadian soldier was killed in a similar suicide attack.