Pentagon officials say three U.S. military members were killed outside a Jordanian military base.
A U.S. official said in Washington on November 4 that one U.S. service member died immediately and two others died of their wounds at a hospital in the capital, Amman.
A Jordanian military officer was also wounded in the incident.
The official spoke on condition of anonymity as details of the incident are still being investigated.
Shots were reportedly fired at a car carrying the Americans when they tried to enter the Al-Jafr base near the southern Jordanian town of Mann, officials said.
It was not clear what prompted the shooting.
Jordan is a key ally of Washington and member of the U.S.-led coalition fighting Islamic State (IS) militants in Iraq and Syria.
One year ago, a Jordanian police captain shot dead two Americans and three others at a training facility in Jordan.