Ukrainian official accused Russian leader Vladimir Putin on Wednesday of trying to widen the conflict in Ukraine.

The assertion came after Washington said Russian fighter jets intercepted a US drone over the Black Sea, causing it to crash.

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The US military said a Russian fighter jet had dumped fuel on an American drone over the Black Sea and then collided with it on Tuesday, causing the drone to crash. The Pentagon slammed the maneuver as "reckless."

According to US European Command, two Russian Su-27 fighters intercepted the unmanned MQ-9 Reaper over international waters and one clipped its propeller.

"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.

"The incident with the American MQ-9 Reaper UAV — provoked by Russia over the Black Sea — is Putin's way of signaling his readiness to expand the conflict to involve other parties.

Moscow has denied causing the crash of the drone. However, Russia's ambassador to the US on Wednesday called on Washington to halt "hostile" flights near his country's border after a US drone was intercepted by Russian fighters over the Black Sea.

"We assume that the United States will refrain from further speculation in the media and stop flights near Russian borders," ambassador Anatoly Antonov wrote on Telegram. "We consider any action with the use of US weaponry as openly hostile."

Russia annexed the Ukrainian peninsula of Crimea in 2014 and considers it its territory. Ukraine and most countries of the world do not recognize the annexation.

US tries to recover fallen drone

The US State Department said it had summoned Russia's ambassador to protest. White House national security spokesman John Kirby said, "obviously, we refute the Russians' denial" and added that the United States is trying to prevent the fallen drone from getting into the wrong hands.

"Without getting into too much detail, what I can say is that we've taken steps to protect our equities with respect to that particular drone," Kirby said. "We obviously don't want to see anybody getting their hands on it beyond us."

Ukraine defends deployment of US drones

Meanwhile, Ukraine's Air Force has defended the deployment of US reconnaissance drones after the incident. "The Black Sea is not an internal sea of Russia, as they have occupied the Sea of Azov and consider it theirs," Ukrainian Air Force spokesman Yuri Ihnat said.

The Black Sea is also bordered by NATO members, including Turkey and Romania, which is why the US drones are operating there on a legal basis, he added.

British Defence Secretary Ben Wallace also urged Moscow to respect international airspace. "The key here is that all parties respect international air space and we urge the Russians to do so," Wallace said at the DSEI Japan defence show in Chiba prefecture, near Tokyo.