WASHINGTON — A fourth American soldier has been found dead after an ambush in Niger this week that killed three United States Army Special Forces and wounded two, American officials said on Friday.

It was not clear whether the American had been captured and killed by militants or whether he had been separated during the fighting that erupted on Wednesday. Special Forces troops were ambushed during what was initially called a routine training mission with Nigerien soldiers by what commanders say was a larger, heavily armed Qaeda force from neighboring Mali.

Local Nigeriens recovered the soldier’s body near the site of the ambush, about 120 miles north of Niamey, the capital of Niger, where the United States now has about 800 troops based, an American military official said.

Asked on Friday whether the United States would retaliate against the militants responsible for the deadly attack, Sarah Huckabee Sanders, the White House press secretary, said, “We’re continuing to review and look into this.”