Moscow warned against "hostile" US flights on Wednesday, as tensions simmered a day after a Russian fighter jet was accused of colliding with an American drone over the Black Sea.
US European Command said two Russian Su-27 fighters intercepted the unmanned MQ-9 Reaper over international waters on Tuesday and one clipped its propeller.
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.
- Regular intercepts -
Russian intercepts over the Black Sea are common, Kirby said 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 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 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.
- 'Unflyable and uncontrollable' -
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 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 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.
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.