"The incident with the American MQ-9 Reaper UAV -- provoked by Russia over the Black Sea -- is Putin's way of signalling his readiness to expand the conflict to involve other parties. The purpose of this all-in tactic is to always be raising the stakes," Ukraine's National Security and Defence Council secretary Oleksiy Danilov said on social media.

Washington blamed Moscow for the incident, calling its fighters' conduct reckless and unprofessional, but Russia has denied any wrongdoing.

"We assume that the United States will refrain from further speculation in the media and stop flights near Russian borders," Russia's ambassador to Washington, Anatoly Antonov, said Wednesday.

"We consider any action with the use of US weaponry as openly hostile," he wrote on social media channel Telegram.

Russia's defence ministry said Tuesday it scrambled fighter jets following the detection of a US drone over the Black Sea and denied causing the crash.

The Pentagon said its drone was on a routine mission when it was intercepted "in a reckless, environmentally unsound and unprofessional manner,", while Russia countered the aircraft was out of control.

"As a result of a sharp manoeuvre... the MQ-9 unmanned aerial vehicle entered an uncontrolled flight with loss of altitude and collided with the surface of the water," the 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 followed up saying, "obviously, we refute the Russians' denial".

He added the United States was trying to prevent the fallen drone from getting into the wrong hands.

"We've taken steps to protect our equities with respect to that particular drone -- that particular aircraft," Kirby told CNN.