The US military confirmed on Thursday that the blast also destroyed two Humvees in which the four were travelling.
The attack occured in the Neka district of Paktika province on Afghanistan's southeastern border with Pakistan.
One of the soldiers was in critical condition, according to a US spokesman in Kabul.
The wounded have been evacuated to Salerno Fire Base in the neighbouring Khost province. The third soldier and the interpreter were both reported to be stable.
There has been no claim of responsibility, but Taliban and other groups opposed to the US military presence are active in Afghanistan's southern provinces.
Rocket attacks and improvised explosive devices are their most common forms of attack.