Western military sources told AFP Tuesday that there had been an "incident" involving a US-made Reaper drone flying over the Black Sea, an area of intense NATO military activity close to the Ukraine war frontlines.

"Something happened but we don't have confirmation that the drone has been shot down. An investigation is underway," one of two Western sources who confirmed "an incident" told AFP.

The sources, who requested anonymity due to the sensitivity of the information, did not say which country was operating the drone, which is used extensively by the United States as well as many of its NATO allies.

Russian Su-27 aircraft allegedly struck propeller of US MQ-9 drone

Later, the US European Command issued a statement saying that "a Russian Su-27 aircraft struck the propeller of a U.S. MQ-9 drone, causing U.S. forces to have to bring the MQ-9 down in international waters."

The Command claimed that "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."

BREAKING: This morning, a Russian Su-27 aircraft struck the propeller of a U.S. MQ-9 drone, causing U.S. forces to have to bring the MQ-9 down in international waters, according to @US_EUCOM.

— Lara Seligman (@laraseligman) March 14, 2023

"This incident demonstrates a lack of competence in addition to being unsafe and unprofessional," it added.

The US European Command insisted that this "follows a pattern of dangerous actions by Russian pilots while interacting with U.S. and Allied aircraft over international airspace, including over the Black Sea."

"These aggressive actions by Russian aircrew are dangerous and could lead to miscalculation and unintended escalation," the statement concluded.

"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," US Air Force General James Hecker also claimed.

Hecker said that "U.S. and Allied aircraft will continue to operate in international airspace," calling on the Russians "to conduct themselves professionally and safely."

"These aggressive actions by Russian aircrew are dangerous and could lead to miscalculation and unintended escalation."

'Unsafe and unprofessional' intercept: White House

On his part, White House Spokesperson John Kirby said US President Joe Biden was briefed on Tuesday about the incident.

Kirby indicated that while there have been other such intercepts, this one was noteworthy because it was "unsafe and unprofessional" and caused the downing of a US aircraft.

"So it's unique in that regard," he said.

"We don't need to have some sort of check-in with the Russians before we fly in international airspace. There's no requirement to do that, nor do we do it," Kirby said.

"The State Department will be speaking directly with their Russian counterparts, and expressing our concerns over this unsafe and unprofessional intercept," he said.

In addition, a NATO official said that the alliance's top military commander has informed allies about the incident.

"General (Christopher) Cavoli has briefed NATO allies on the incident today," the official told Reuters.