Authorities now say two Marines have died in Afghanistan, as the U.S. conducts its largest Marine operation there since 2001.
The military initially said four troops had died, but now says the deaths were counted twice by mistake.
A third U.S. service member died Friday from wounds suffered last month.
Thousands of American troops have been taking part in the massive anti-Taliban offensive. They've met little direct resistance but are vulnerable to guerrilla tactics like suicide or roadside bombings.
The latest casualties bring to 104 the number of U.S. troops killed in Afghanistan this year, a record pace. The deaths come after eight British deaths in Afghanistan in a 24-hour period. Britain has now lost more troops in Afghanistan than in Iraq.
Violence has been flaring all Afghanistan, with nearly two dozen other people reported killed today in bomb blasts and gun battles.