One US soldier was missing following the blast, Central Command said in a statement on Thursday, adding that three US soldiers and an interpreter were injured.

"The soldiers were working around a weapons cache when the
explosion occurred," the statement said. "The wounded soldiers were evacuated to the 452nd Combat Support Hospital at Bagram Air Base," near Kabul.

It said an investigation of the explosion had been opened.

A US military spokesman in Kabul confirmed the details and said that the explosion occurred at about 3:00 pm (12:30 GMT). 

"All I can add is that the wounded soldiers and interpreter are
receiving the best medical care possible and we extend out
condolences to the families of these brave warriors who were
fighting for peace in Afghanistan," Lieutenant Colonel Bryan
Hilferty said. 

Worsening Security

The seven deaths bring to 107 the number of US soldiers killed while involved with Operation Enduring Freedom although not all of those deaths were in Afghanistan.

The incident came amid deteriorating security across Afghanistan. The war-torn country's southern and southeastern parts have particularly witnessed a number of attacks and kidnappings.

On Tuesday, a Canadian peacekeeper was killed and three others injured when explosives were detonated near their patrol. Also, a bomb blast in Kandahar on 6 January killed 15 people and injured many.