Two other soldiers were wounded in the attack in Kandahar province, according to NATO’s Resolute Support mission in the country.
The US occupation spokesman said the names of those killed were being withheld pending notification of next of kin.
The troops were on patrol near Kandahar airport in Dand district, provincial police spokesman Jamal Nasir Barkzai told AFP.
The Taliban claimed responsibility for the attack, with spokesman Zabihullah Mujahid saying on Twitter that the blast destroyed the vehicle and killed all on board.