Three US military trainers have been shot dead in Jordan 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 says.
Friday's 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.
Many ordinary Jordanians harbour strong anti-American sentiment over Washington's strong support for Israel and its military interventions in the region.
A Pentagon spokesperson confirmed the shooting incident.
"We are saddened to report that three US service members were killed today in a shooting incident at a Jordanian military base," Peter Cook said, adding more information would be provided "as appropriate".
Since the start of the Syrian conflict in 2011, Washington has spent millions of dollars to help Jordan set up an elaborate surveillance system known as the Border Security Program to stem infiltration by militants from Syria and Iraq.
The last incident involving US personnel was in November last year when a Jordanian officer shot dead two US government security contractors and a South African at a US-funded police training facility near Amman before being gunned down.
The gunman was later said by security sources to have been a sympathiser of Islamic State with strong anti-Western feelings.