The Ukrainian Defense Forces do not believe pilot error was behind the incident, the source added.
Pilot Oleksiy Mes, known as “Moonfish,” was killed in the crash while “repelling the biggest ever aerial attack” by Russia against Ukraine, said the source, adding that the pilot was buried on Thursday.
The crash is being investigated and international experts will be invited to participate in the probe, the source added.
Ukraine's President Volodymyr Zelensky has long demanded the F-16s to aid his country's fight agains Russia.
The death of the pilot is a major blow for Ukraine. The first F-16s only arrived in the country earlier this month and Moonfish was one of the few pilots trained to fly them.
Ukrainian President Volodymyr Zelensky said on Tuesday that the Ukrainian Air Force used the F-16 to destroy missiles and drones launched by Russia on Monday, the first time any Ukrainian official confirmed the jets were being used in combat.
Kyiv waited a long time to get hold of the F-16s, and Zelensky has been asking its Western allies for the fighter jets since the start of the full-scale invasion.
But as with other equipment, Western countries hesitated before finally agreeing to provide F-16s. The Netherlands and Denmark pledged to provide them early summer in 2023, but it took another few weeks for the United States to green-light the transfer.
When they arrived earlier this summer, Zelensky said he and his government held “hundreds of meetings and negotiations” to secure the jets.
A group of Ukrainian pilots started their F-16 training in the US in the fall. While it can take years to get fully trained up to fly the planes, Moonfish and others had to do it in six months.
Ukraine is hoping the F-16 will give it a much-needed boost. The jets are multi-role: they can provide air cover for troops, attack ground targets, take on enemy planes and intercept missiles. With the right armament, F-16s could deter Russian fighter-bombers from approaching the battlefield.
Still, the jets are no silver bullet. Ukraine can use them to deny Russia control over the skies, but experts say their capabilities are inferior to the most modern Russian combat aircraft that would likely prevail in an air battle with the F-16.
Moonfish and another pilot Andriy Pilshchikov, known by the call sign “Juice,” became the faces of Ukraine’s campaign to get the F-16s.
It was an uphill battle, but Juice and Moonfish pulled through it together. They were young and enthusiastic, spoke good English and were willing to fight to get the US jets into Ukrainian skies.
Flying the F-16 was their dream and when Juice died in a plane crash during a combat mission last August, Moonfish made it his goal to fulfill it.
Of the two, Moonfish was the quiet one: an aviation geek not keen on publicity. But when Juice died, Moonfish had to take his place. In a rare interview with CNN, he admitted that if Juice were alive, he’d be giving interviews.
A man of few words, passionate about his job, he had his emotions under control. A straight talker who knew everything about F-16s.
“Andriy was the ‘ideas man’ and the main driving force behind it all,” Moonfish said. “And I feel responsible to him for ensuring these planes arrive.”
Speaking to CNN while in training, he said it was necessary for him and other Ukrainian pilots to undergo a truncated version of the training. “We would have had a lot of time to study the jet completely in peacetime, but we do not have the time,” he said.
In a statement issued later on Thursday, the Ukrainian Air Force said Moonfish destroyed three cruise missiles and one attack drone on Monday, before he was killed the crash. The air force said he was posthumously awarded the rank of colonel.
Belgium has promised to send 30 F-16 fighter jets to Ukraine by 2028 in the latest defence pledge by a Nato member to Kyiv, demonstrating allies’ resolve in the face of Russia’s intensifying assault on the country.
But Ukraine’s President Volodymyr Zelenskyy repeated his demand for western allies to lift restrictions on the use of supplied weaponry to hit targets in Russia, saying it was “unfair” that Ukraine could not strike back against long-range missile strikes on its cities.
Zelenskyy has pleaded for US-made Patriot systems capable of shooting down Russian missiles and planes that launch powerful glide bombs on Ukrainian military positions and cities. Ukraine’s air force has said the only way to halt their use is to be able to shoot down the aircraft carrying the bombs while they are in Russia with long-range air defence systems and F-16s.
Belgian Prime Minister Alexander De Croo made clear that the F-16s were being supplied under an agreement that would only allow them to be used in the “territory of Ukraine”.
Usage of western weapons to strike Russia has become an increasingly contentious issue as some Nato members fear that such a move would mark an escalation of the conflict.
“[Vladimir] Putin has only one influence mechanism, that is the destruction of life. He is not capable of anything else,” Zelenskyy said at a joint press conference in Brussels. “A sufficient power of weaponry is crucial so that we can physically defend [ourselves] against Russia’s terror.”
“They are shooting at you, and you cannot shoot back at them because you do not have the permission [from western partners],” he added.
Ukraine’s western allies are under intense pressure to step up supplies of weaponry, particularly artillery and air defence systems, as Russia seeks to make further territorial gains in the country’s east while also subjecting Ukrainian cities to daily bombing raids.
