An Afghan interpreter was also wounded in the blast, which hit a US armoured vehicle on Friday in the Urgun district in Paktika province, the US military said in a statement.
The wounded were evacuated by helicopter to a US base for treatment, the statement said. The attack occurred as the convoy was returning from the village of Gayan. The military has started an investigation.
The names of the dead were withheld pending notification of kin.
The deaths brought to 147 the number of US soldiers killed in and around Afghanistan since the US invaded the Asian country in what was called Operation Enduring Freedom in 2001.
Meanwhile, two suspected Taliban fighters were killed and four wounded in a gun battle after an Afghan police convoy was allegedly ambushed.
Afghan police said the clash occurred late on Friday at Mizan in the southern province of Zabul when police were escorting an Afghan engineer back to the provincial capital of Qalat.
A Taliban spokesman said seven
policemen were killed
"During a one-hour battle, two Taliban were killed and four were wounded after the Taliban ambushed a government police unit who were evacuating a local engineer from Mizan to Qalat," Mizan district chief Rahmatullah Khan said.
He said no police or government soldiers were wounded.
Taliban spokesman Abd al-Latif Hakimi claimed responsibility for the ambush by telephone and said the Taliban had killed seven policemen.
In a separate statement, the US military said Afghan army forces on Friday captured a suspected bomb-maker and former Taliban member in the west of the country.