Russia said on Wednesday that it would try to retrieve the remnants of a US drone that crashed into the Black Sea.
The large MQ-9 Reaper drone plunged into the water on Tuesday.
The US said it brought down the damaged drone after it became "unflyable" when a Russian jet clipped its propeller - but Moscow has denied these claims.
Speaking on state television, Russian security council secretary Nikolai Patrushev confirmed Moscow was attempting to find the aircraft.
"I don't know whether we'll be able to retrieve it or not but it has to be done," Mr Patrushev said.
He also said that the drone's presence in the Black Sea was "confirmation" that the US was supporting Ukraine in the war.
"The Americans say all the time that they are not involved in the hostilities... this is another confirmation that they are directly taking part in these activities, in the war," he said.
Senior Washington official John Kirby said the US was also searching for the aircraft, but stressed that if Russia beat them to it, "their ability to exploit useful intelligence will be highly minimised".
Speaking to ABC America's morning news programme, Good Morning America, he added that there were logistical challenges as it crashed in "very deep water".
US military officials said the incident happened on Tuesday morning and the confrontation lasted around 30-40 minutes.
In a statement, the US said Russian jets dumped fuel on the drone several times before the collision.
Pentagon spokesman Brig Gen Pat Ryder told reporters the drone was "unflyable and uncontrollable", adding the collision also likely damaged the Russian aircraft.
Russia has denied its two Su-27 fighter jets made any contact with the US drone.
Russia's defence ministry said the drone crashed after a "sharp manoeuvre", and that it was flying with its transponders (communication devices) turned off.
The US and UK have previously gone to extraordinary lengths to recover their technology after crashes.
They retrieved the wreckage of their stealth fighter jet, the F-35 from the bottom of the South China Sea after it sank.
But on the face of it, the Pentagon seems more relaxed about losing a Reaper drone. It's older technology and numerous have been lost before.
And trying to recover a downed drone in deep waters, next to a war zone, with Russian ships and submarines patrolling, could present even greater risks of escalation.
Tensions have risen over the Black Sea ever since Russia's annexation of nearby Crimea in 2014.
And since Russia's full-scale invasion of Ukraine, the US and the UK have stepped up surveillance flights, though always operating in international airspace.
The lost Reaper may have been carrying a surveillance pod able to suck up electronic data such as radar emissions.
The US Department of Defense said in a press release that the surveillance trips are used to gather information which helps improve security for Europe and supports "allied partners".
The US has reportedly shared intelligence with Ukraine previously, including to help it sink a Russian ship in the Black Sea.
