A Russian fighter jet on Tuesday dumped fuel on an American drone over the Black Sea then collided with it, causing the drone to crash, the US military said.
US European Command said two Russian Su-27 fighters intercepted the unmanned MQ-9 Reaper over international waters and one clipped its propeller.
"Several times before the collision, the Su-27s dumped fuel on and flew in front of the MQ-9 in a reckless, environmentally unsound and unprofessional manner," it said.
The statement confirmed an earlier report by AFP of an incident involving a US-made drone in the area.
Russian intercepts over the Black Sea were common, US National Security Council spokesman John Kirby told journalists in Washington, but this one "is noteworthy because of how unsafe and unprofessional it was, indeed reckless that it was".
NATO diplomats in Brussels confirmed the incident, but said they did not expect it to immediately escalate into a further confrontation.
A Western military source, speaking to AFP on condition of anonymity, said that diplomatic channels between Russia and the United States could help limit any fall-out.
"To my mind, diplomatic channels will mitigate this," the source said.
Russia's invasion of Ukraine in February last year has led to heightened fears of a direct confrontation between Moscow and the Western NATO military alliance, which has been arming Kyiv to help it defend itself.
News of a missile strike in eastern Poland in November last year briefly caused alarm before Western military sources concluded that it was a Ukrainian air defence missile that had malfunctioned, not a Russian one.
There was no immediate reaction from Moscow.
- 'Unsafe and unprofessional' -
The United States uses MQ-9 Reapers for both surveillance and strikes, and has long operated over the Black Sea keeping an eye on Russian naval forces.
"Our MQ-9 aircraft was conducting routine operations in international airspace when it was intercepted and hit by a Russian aircraft, resulting in a crash and complete loss of the MQ-9," said US Air Force General James Hecker, commander of US Air Forces Europe and Air Forces Africa.
"In fact, this unsafe and unprofessional act by the Russians nearly caused both aircraft to crash.
"US and allied aircraft will continue to operate in international airspace and we call on the Russians to conduct themselves professionally and safely," he added.
The US statement said that pilots had brought the Reaper down in international waters, while the US Naval Institute said it had crashed off the coast of Odessa in southeast Ukraine.
Several US Reapers have been lost in recent years, including to hostile fire.
One was shot down in 2019 over Yemen with a surface-to-air missile fired by Huthi rebels, the US Central Command said at the time.
According to media reports, a US MQ-9 crashed in Libya in 2022, while another went down during a training exercise in Romania earlier in the same year.
Reapers can be armed with Hellfire missiles as well as laser-guided bombs and can fly for more than 1,100 miles (1,770 kilometres) at altitudes of up to 15,000 metres (50,000 feet), according to the US Air Force.