A blast that killed seven US soldiers in Afghanistan may have been caused by a booby-trap, the US military says.
The soldiers died while investigating a weapons cache in a village near Ghazni, east Afghanistan, on Thursday.
The exact cause of the blast had not been established and an investigation was continuing, said US spokesman Lieutenant Colonel Brian Hilferty.
The US has lost a number of troops while hunting militants in southern and eastern Afghanistan.
Colonel Hilferty said it was unclear how the men found the weapons cache.
"
This has been a costly week for both the coalition and
for Isaf
"
Colonel Brian Hilferty
US military spokesman
Another US soldier was still missing after Thursday's explosion, but three wounded Americans and an Afghan interpreter had been released from hospital, he added.
President Hamid Karzai offered his condolences to US President George W Bush, saying: "It is another sacrifice of your soldiers for peace and stability in Afghanistan."
A local official from Ghazni said the weapons had exploded by accident while the American soldiers were transporting them.
Major US presence
The BBC's Andrew North, in Kabul, said initial reports suggest that the soldiers were trying to move weapons from the cache when they detonated.
The US military leads a 12,000-strong force in Afghanistan hunting Taleban and al-Qaeda members still in the country since the US-led campaign removed the Taleban from power in 2001.
In the last few days, Kabul has been the focus of suicide bomb attacks said to have been carried out by the ousted Taleban.
A British soldier was killed in the Afghan capital on Wednesday when a car laden with explosives hit his vehicle.
On Tuesday a suicide bombing in the city killed a Canadian member of the international peacekeeping force.
"This has been a costly week for both the coalition and for Isaf," Colonel Hilferty said.
"But our long-term commitment to the people of Afghanistan is unwavering. We will win. There is no other option."
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