Three US troops were killed in a shooting attack outside a Jordanian training facility on Friday, a US official said, following earlier reports that one or two US personnel were dead.
"A total of three US service members died today in the incident in Jordan," the official said. "Initial reports were that one was killed, two injured. The two injured service members were transported to a hospital in Amman, where they died."
"The service members were in vehicles approaching the gate of a Jordanian military training facility, where they came under small arms fire," the official added.
"We are working with the Jordanian government to gather additional details about what happened."
The shooting took place at the gate of the Prince Faisal airbase in al-Jafr, southern Jordan, when the car carrying the US trainers failed to stop, the Jordanian army said, adding that a Jordanian officer was also wounded.
READ MORE: Gunman kills five at Jordan police training centre
Jordan, a key US ally in the Middle East, is a member of the US-led coalition fighting the Islamic State in Iraq and the Levant (ISIL) in neighbouring Syria and Iraq.
US forces have trained a small group of vetted Syrian rebels in Jordan, and American instructors have trained Iraqi and Palestinian security forces in Jordan as well over the past few years.
The White House said on Friday it would work with Jordan to determine the circumstances that led to the shooting deaths of three US military trainers.
"The United States is quite interested in getting to the bottom of what exactly occurred. Our expectation is that the government and military officials in Jordan will assist us in that investigation," White House spokesman Josh Earnest told reporters.
Friday's incident comes almost a year after a Jordanian policeman shot dead two US instructors, a South African and two Jordanians at a police training centre east of Amman, before being gunned down.
Washington said at the time that the two Americans killed in the November 9, 2015 shooting were employees of the private firm DynCorp contracted by the State Department to train Palestinian forces.
Two other Americans were wounded in that incident, which sparked concern in Washington and was condemned by the US embassy.
Last year, the US announced its intention to increase overall assistance to Jordan from $660m to $1bn annually for the 2015-2017 period.
A government source told AFP that military training is provided at al-Jafr airbase by instructors of various nationalities, including Americans, to participants from different countries.
Source: Al Jazeera News And Agencies