Ukraine lost an F-16 and a top pilot after one of the fighter jets crashed while battling Russian missiles

• A Ukrainian F-16 crashed on Monday, killing a top pilot, according to the Ukrainian military.
• The crash occurred during a massive Russian attack, which Ukraine's F-16s helped to defend against.
• It marks Kyiv's first loss of the US-made aircraft just weeks after they arrived in the country.

A Ukrainian F-16 fighter jet crashed on Monday, killing a top pilot in what appears to mark Kyiv's first loss of the American-made aircraft.

It is still unclear what led to the crash, which occurred just weeks after Ukraine received its first batch of F-16s from NATO.

The Ukrainian Air Force confirmed on Thursday that one of its pilots, Oleksiy Mes, died in combat during a massive Russian attack on Monday. Kyiv said he shot down three cruise missiles and one attack drone before he was killed.

"Oleksiy saved Ukrainians from deadly Russian missiles," the Ukrainian Air Force wrote in a Telegram statement. "Unfortunately, at the cost of his own life."

The Ukrainian military said it lost communication with an F-16 while it was engaging the Russian threats and later found out that the aircraft had crashed. It said that the cause of the "accident" is under investigation.

Initial reports suggested the jet wasn't downed by Russian fire, a US official told The Wall Street Journal, which first reported the loss of the aircraft. A source in the Ukrainian Defense Forces told CNN that they don't think pilot error caused the crash.

The Pentagon and US European Command referred questions to the Ukrainian military, and Kyiv's air force did not immediately respond to Business Insider's queries.

The fatal incident reportedly took place during Monday's massive Russian missile and drone attack , during which Moscow launched a combined 236 munitions in what Ukraine said was the largest aerial bombardment it had faced throughout the war.

Ukrainian President Volodymyr Zelenskyy later shared that Kyiv used its F-16s for the first time in combat that day to shoot down several Russian missiles. He said the fighter jets "performed well."

The F-16 crash and death of a pilot is a major blow to Ukraine, which has waited years to get the fighter jets. After the US allowed its European allies to transfer the aircraft to Kyiv last year, Western countries began training a limited number of Ukrainian pilots to fly them.

Ukraine revealed in early August that the first F-16s had arrived. However, Kyiv is only operating a small number of fighter jets, and Zelenskyy has expressed concerns that the country won't receive enough to make a difference in combat.