A U.S. military Black Hawk helicopter crashed off the southern coast of Yemen while training its crew, leaving one service member missing, officials said.

Five others aboard the aircraft were rescued, officials said in a statement issued by U.S. Central Command.

The crash took place Friday evening. Officials said the crash was under investigation.

Asked if the crash involved another special forces raid, Central Command told The Associated Press that “this was a routine training event specifically for U.S. military personnel.”

“Training events such as this are routinely held by U.S. forces within a theater of operations in order to maintain their proficiency within the operating environment,” CENTCOM told the AP in a statement. “Commanders deemed this location appropriate and safe for a routine training event, considering both the operational environment and weather conditions at the time.”

Yemen, located on the southern end of the Arabian Peninsula, is the Arab world’s poorest country and is engulfed in a yearslong civil war.

The war pits Shiite rebels known as Houthis and their allies against a Saudi-led coalition backing the country’s internationally recognized government. The U.S. has provided targeting and logistical support to the Saudi-led coalition, which faces criticism over its airstrikes killing civilians caught up in the conflict.

Yemen is also home to what the U.S. considers the most dangerous branch of the al-Qaida terror network. U.S. special forces backed with Emirati troops launched a raid in Yemen in January under President Donald Trump that killed a U.S. Navy SEAL and 30 other people, including women, children and an estimated 14 militants.

(AP)