Three U.S. servicemen were killed and three wounded when an improvised explosive device detonated on Tuesday near the central Afghan city of Ghazni, the NATO-led Resolute Support mission said in a statement.
The Taliban, which control large parts of Ghazni Province, claimed responsibility for the attack, which also wounded an American civilian contractor.
The NATO statement gave no details but Mohammad Arif Noori, a spokesman for the provincial governor, said an armored vehicle carrying U.S. troops hit a large roadside bomb in Shahbaz area, just outside the city on Tuesday morning.
He said U.S. Special Forces had been conducting operations with Afghan forces around Ghazni city since Monday.
The deaths are the latest in a growing toll on U.S. forces in Afghanistan following the death of an army Ranger during an operation against al Qaida terrorists in Nimruz Province on Saturday. Resolute Support said the soldier had been accidentally shot by a member of Afghan partner forces.
At least 11 U.S. servicemen have now died in Afghanistan this year, in combat or in so-called “insider attacks” by Afghan soldiers or police.
Four Czech soldiers, serving with Resolute Support, have also been killed.
There was no official confirmation of the circumstances of the blast but Ghazni has been one of the most heavily fought over regions of Afghanistan this year and many areas close to the city are in the hands of the Taliban.
The city, which sits on the main highway linking the capital Kabul with Kandahar in the south, was overrun this year by a large Taliban force before it was driven off by Afghan and U.S. troops after days of heavy fighting.
About 14,000 U.S. troops remain in Afghanistan as part of Resolute Support and a separate counterterrorism mission aimed against militant groups such as al Qaida and Islamic State terror groups.