Three US servicemen were shot and killed at a Jordanian training facility on Friday. The servicemen were in a vehicle approaching the entrance gate to the Prince Faisal airbase in Al Jafr, Jordan when they came under fire from friendly forces inside the base.

The US Embassy in Amman issued a statement saying: “We have received reports about a security incident involving US personnel. We are in contact with the appropriate Jordanian authorities, who have offered their full support. We will report more information when available and appropriate.”

The facility in Jordan was established last year by the US to train moderate Syrian rebels to fight the Islamic State (ISIS). AFP news agency quoted a US defense official as saying it was a “green on blue” incident, a military term for when friendly forces attack US personnel.”But we can’t say for the moment if it was a deliberate” act to kill US personnel or “some kind of misunderstanding,” the official told the news agency.

One year ago, a Jordanian officer shot dead two U.S. government security contractors, a South African trainer and two Jordanians, at a U.S. funded police training facility near Amman. The Jordanian officer was killed in the ensuing gun battle, and was buried a few days later while crowds chanted, “Death to America”.

That incident took place on November 9th, the anniversary of the deadliest Al Qaeda attack in Jordan’s history. The 2005 Amman bombings were a series of coordinated bomb attacks on three hotel lobbies  that killed 60 people and injured 115 others. It is unclear whether the timing of this attack is connected to that event.