Moscow said on Wednesday it would try to retrieve the wreckage of a U.S. military drone that crashed over the Black Sea in a confrontation that Washington blamed on two Russian fighter jets.
Russia also warned against "hostile" U.S. flights as tensions simmered and Russia denied its Su-27 military aircraft had clipped the propeller of the unmanned Reaper drone.
Kyiv meanwhile countered that the incident over international waters was evidence the Kremlin wants to draw the U.S. into the conflict in Ukraine.
"I don't know whether we'll be able to retrieve it or not but it has to be done. And we will certainly work on it," Russian Security Council secretary Nikolai Patrushev said in televised remarks.
The crash on Tuesday, which Washington said was the fault of reckless and unprofessional Russian conduct, further ratcheted up tensions between Moscow and Western allies, already soaring over the Ukraine conflict.
Mr. Patrushev said the incident was further proof that the U.S. is a direct party to fighting between Moscow and Kyiv and said Russia had a responsibility to "defend our independence and our sovereignty".
Russia's Defence Ministry said it had scrambled jets after detecting a U.S. drone over the Black Sea and denied causing the crash.
The Pentagon said the drone was on a routine mission when it was intercepted "in a reckless, environmentally unsound and unprofessional manner".
Russia said the aircraft had lost control but White House national security spokesman John Kirby said the U.S. "obviously" refuted the denial.
He added the U.S. 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," Mr. Kirby told CNN.
Russian intercepts over the Black Sea are common, Mr. Kirby said, but this one was particularly "unsafe and unprofessional" and "reckless".
Ukraine said the incident was "provoked by Russia" and cautioned that it signalled President Vladimir Putin's aim to "expand the conflict".
"The purpose of this all-in tactic is to always be raising the stakes," Ukrainian National Security and Defence Council secretary Oleksiy Danilov said on social media.
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 diplomatic channels between Russia and the U.S. could help limit any fallout.
"To my mind, diplomatic channels will mitigate this," the source said.
Russia's campaign in Ukraine has led to heightened fears of a direct confrontation between Moscow and the NATO alliance, which has been arming Kyiv to help it defend itself.
Reports of a missile strike in eastern Poland in November briefly caused alarm before Western military sources concluded it was a Ukrainian air defence missile, not a Russian one.
The U.S. 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 U.S. 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.
"U.S. 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 said 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.
Several U.S. 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 U.S. Central Command said at the time.
Reapers can be armed with Hellfire missiles as well as laser-guided bombs and can fly for more than 1,770 kilometres at altitudes of up to 15,000 metres, according to the U.S. Air Force.