An Air Force F-16 fighter jet crashed in the Middle East late Sunday, killing the pilot on board, U.S. military officials said Monday.

The plane was returning to its base shortly after taking off on a combat mission, said Army Col. Steve Warren, a Pentagon spokesman. Officials with U.S. Central Command called it a “non-combat related incident,” indicating the plane likely experienced mechanical problems. The 11 p.m. crash did not occur in Iraq or Syria, where the United States has been launching airstrikes on the Islamic State militant group for months. The incident is under investigation, officials said.

U.S. officials would not say where the aircraft crashed. The Air Force was working to notify the pilot’s family on Monday.

Recent airstrikes in Iraq and Syria have been carried out from several bases in the Persian Gulf region, including Al Udeid Air Base in Qatar, Ali al Salem Air Base in Kuwait and al Dhafra Air Base in the United Arab Emirates. Warren declined to say which base was used to launch the F-16, saying it is Defense Department policy not to do so.

Craig Whitlock contributed to this report.