GHAZNI, Afghanistan — American forces experienced the worst loss of life so far this year in Afghanistan when three soldiers were killed in a Taliban bombing on Tuesday. Three more soldiers and an American contractor were wounded.

The deaths took place when a roadside bomb went off near Ghazni City, in the southeastern province of the same name, killing Special Forces soldiers three months after they were sent to save that city from falling to the Taliban.

The Pentagon declared an end to American combat operations in Afghanistan in 2014. But since that time, the Taliban have expanded their reach, and the Americans have rejoined the fray.

A witness said the bomb in Ghazni went off as an American convoy passed on the highway. “The convoy set off a roadside mine, and there was smoke all over the place,” said the witness, Haji Abdulamin, a local resident. “The road was blocked, and a few minutes later helicopters landed and took the dead.”