Three US military trainers were shot dead in Jordan on Friday when their car failed to stop at the gate of a military base and was fired on by Jordanian security forces, a Jordanian military source said.
The incident occurred at the Prince Faisal air base in the south of the country, a close ally of the United States. Two trainers died immediately and a third died later in hospital.
A Jordanian army guard was also shot and wounded.
"There was an exchange of fire at the entrance to the base after an attempt by the trainers' vehicle to enter the gate without heeding orders of the guards to stop," the military source said.
"An investigation is now under way to know exactly what happened."
Another Jordanian security source said it was not possible to rule out political motives in the incident at an air base where dozens of US trainers work alongside Jordanians.
US officials, speaking on condition of anonymity, told Reuters they were reviewing the incident and could not rule out the possibility of a deliberate attack.
One said there were Americans in the convoy who were unharmed in the incident.
Many ordinary Jordanians harbor strong anti-American sentiment over Washington's strong support for Israel and its military interventions in the region.