A Ukraine Air Force Su-27 fighter jet crashed on Tuesday, October 16 during large-scale NATO aerial exercises, the Ukrainian military said.

“Today, at about 17:00, an Su-27 fighter jet crashed during a combat training flight in the area of Ulaniv [between the Berdychiv and Khmilnyk],” the the General Staff of the Armed Forces of Ukraine said in a Facebook post.

“Search and rescue activities are being carried out,” the General Staff added.

The bodies of both pilots were found, the military said later.

U.S. Air Forces in Europe and Air Forces Africa later confirmed that “a U.S. service member was involved” in the incident, adding that it was under investigation.

Exercise Clear Sky 2018 kicked off in western Ukraine on October 8 and is scheduled to run until October 19.

Some 700 troops are taking part, half of them from NATO member countries including the Netherlands, Poland, Romania, the United Kingdom and the United States.

Denmark and Estonia, not NATO members, are also participating.

Ukraine is contributing about 30 aircraft and 350 military personnel in five tactical aviation units.

This story was updated at 1559 GMT on October 16 to include the deaths of the two pilots, and later to include the U.S. Air Force statement.