A Ukrainian F-16 jet fighter was destroyed in a crash Monday, according to a U.S. official, just weeks after the first of the American-made aircraft arrived in Ukraine.

Initial reports indicate the jet wasn’t shot down by enemy fire, although the incident occurred during a massive Russian missile barrage across the country Monday, the official said. Rather, the crash was likely a result of pilot error.

Ukraine used the jets for the first time in combat to shoot down Russian missiles during the strikes this week, according to President Volodymyr Zelensky .

The Ukrainian Air Force wouldn’t confirm the crash or the status of the pilot. The Pentagon referred questions to the Ukrainian Air Force for comment.

But Ihor Polishchuk, the mayor of Lutsk, a city in northwest Ukraine, said this week that Ukrainian Air Force pilot Oleksiy Mes died on Monday during a combat mission. Mes was one of the first Ukrainian pilots to be trained on the F-16. His call sign was “Moonfish” and he frequently appeared  in the media  and visited Washington to lobby the U.S. to send Ukraine the jet fighters.

The news that one of Ukraine’s few F-16s has been destroyed is a major blow to Kyiv, which had pleaded for the jets for months before President Biden finally gave the green light for European countries to transfer the aircraft last year.

Kyiv hopes the advanced Western aircraft will give its forces an edge on the battlefield , particularly to shoot down incoming Russian missiles and help protect troops on the front lines. But they are also vulnerable to Russian air-defense missiles and present a high-value target for Moscow’s forces.

Zelensky announced Aug. 4 that the first of 80 promised F-16s had arrived in Ukraine. The Ukrainian air Force didn’t provide numbers, but a second U.S. official said a total of six aircraft had arrived and Ukraine has six pilots trained to fly them.

Write to Lara Seligman at lara.seligman@wsj.com