A Russian fighter jet on Tuesday dumped fuel on an American drone over the Black Sea and then collided with it, causing the drone to crash, the US military said, according to AFP.
The US military described the maneuver as "reckless".
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.
Moscow denied causing the crash of the drone, which the Pentagon said was on a routine ISR (intelligence, surveillance, reconnaissance) mission.
"As a result of a sharp maneuver... the MQ-9 unmanned aerial vehicle entered an uncontrolled flight with loss of altitude and collided with the surface of the water," the Russian Defense Ministry said, adding that the two Russian jets had no contact with the US aircraft and did not use their weapons.
The US State Department said it had summoned Russia's ambassador to protest.
White House national security spokesman John Kirby later said, "obviously, we refute the Russians' denial" and added that the United States is trying to prevent the fallen drone from getting into the wrong hands.
"Without getting into too much detail, what I can say is that we've taken steps to protect our equities with respect to that particular drone -– that particular aircraft," Kirby was quoted as having told CNN.
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.
Pentagon spokesman Brigadier General Pat Ryder told journalists the drone was "unflyable and uncontrollable so we brought it down", adding that the collision also likely damaged the Russian aircraft, which he said was able to land following the incident.
Anatoly Antonov, the Russian ambassador to the United States, said on Tuesday night that Moscow views the incident as “provocation”
"We view this incident as a provocation," Antonov said after being summoned by the US State Department, according to Reuters.
Antonov said his meeting at the State Department was "constructive" and the issue of possible "consequences" for Moscow over the incident was not raised, RIA reported.
"As for us, we do not want any confrontation between the United States and Russia. We are in favor of building pragmatic relations for the benefit of the Russian and American peoples," Antonov was quoted as saying.
