Three U.S. servicemen were killed in Jordan on Friday when they came under fire while entering a military base, the Pentagon said.
The service members were on a training mission, and the incident occurred as they drove their vehicles into the facility, Pentagon Press Secretary Peter Cook said in a statement.
"We are working closely with the government of Jordan to determine exactly what happened," he added.
The Jordanian news agency Petra initially described the incident as an "exchange of gunfire" at the King Feisal airbase in Al Jafr, southern Jordan.
Jordan is a key U.S. ally in the Middle East and has been a close partner in efforts to combat the rise of the Islamic State in the region.
The Pentagon has not disclosed how many U.S. troops are in Jordan but a small number are involved in support and training missions connected to the fight against the Islamic State in Iraq and Syria.
Contributing: Tom Vanden Brook in Washington