Two US military trainers were shot dead in Jordan on Friday when the car they were in failed to stop at the gate of a military base and was fired on by Jordanian security forces, a Jordanian army source said.

"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 told Reuters news agency.

A third American and a Jordanian officer were reportedly wounded in the exchange of fire, according to AFP.

The US embassy in Jordan confirmed the incident, which occurred at the Prince Faisal airbase in al-Jafr, southern Jordan.

"We have reports of a security incident involving American personnel and we are in contact with Jordanian officials who are giving us all the support," the embassy said in a statement.

US Pentagon spokesman Christopher Sherwood told Al Jazeera that an investigation into the incident was ongoing.

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.

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