Washington’s top general said the crash of a U.S. surveillance drone after being intercepted by Russian jets showed Moscow’s increasingly aggressive behaviour while Russia warned Washington that flying drones near Crimea risked escalation.

A day after the U.S. drone went down over the Black Sea, defence ministers and military chiefs from the U.S. and Russia held rare telephone conversations on Wednesday with relations at their lowest point in decades over Moscow’s invasion of Ukraine.

Moscow’s Defence Minister Sergei Shoigu told his U.S. counterpart, Lloyd Austin, that American drone flights by Crimea’s coast "were provocative in nature" and could lead to ”an escalation … in the Black Sea zone,” a ministry statement said.

Russia, the statement said, "had no interest in such a development but will in future react in due proportion."

Crimea is a peninsula that was part of Ukraine until Moscow annexed it by force in 2014.

Austin declined to offer any details of the call — including whether he criticized the Russian intercept.

But he reiterated at a news conference that the U.S. intended to continue flying where international law allowed and demanded Russian military aircraft operate in a safe and professional manner.

The statement from Russia’s defence ministry said the two countries should ”act with a maximum of responsibility” including by having military lines of communication in a crisis.

Austin appeared before reporters at the Pentagon alongside General Mark Milley, chairman of the Joint Chiefs of Staff, who had a separate call with Russia’s Valery Gerasimov, chief of the General Staff of the Russian Armed Forces.

Trading accusations

The U.S. military has said two Russian Su-27 fighter planes approached its MQ-9 Reaper drone on a reconnaissance mission over the Black Sea’s international waters on Tuesday. The fighters harassed the drone and sprayed fuel on it before one clipped the drone’s propeller, causing it to crash into the sea.

According to Russia, there was no collision. The drone crashed after making ”sharp manoeuvres,” having ”deliberately and provocatively” flown close to Russian air space. Moscow had scrambled its fighters to identify it.

”There is a pattern of behaviour recently where there is a little bit more aggressive actions being conducted by the Russians,” Milley told reporters, saying it was unclear whether the Russian pilots intended to strike the drone.

Earlier, State Department spokesperson Ned Price, speaking to MSNBC, said the incident was likely to have been an unintentional act by Russia.

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While battles between Ukrainian troops and Russian forces raged on in eastern Ukraine, the drone incident on Tuesday was the first known direct U.S.-Russia encounter since Moscow’s invasion of Ukraine about a year ago.

Russia said the episode showed the U.S. was directly participating in the Ukraine war, something the West has taken pains to avoid.

”The Americans keep saying they’re not taking part in military operations. This is the latest confirmation that they are directly participating in these activities – in the war,” Kremlin Security Council Secretary Nikolai Patrushev said.

Bakhmut battle continues

The United States has supported Ukraine with tens of billions of dollars in military aid but says its troops have not become directly engaged in the war, which Moscow portrays as a conflict against the combined might of the West.

Russia’s ambassador to Washington, Anatoly Antonov, accused Washington of deploying drones to collect intelligence that the Kyiv government could use against Russia.

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”The unacceptable activity of the U.S. military in the close proximity to our borders is a cause for concern,” he said in a statement.

He told Washington: ”Stop making sorties near the Russian borders.”

Kyiv, for its part, said the drone crash showed Moscow was willing to expand the conflict zone to draw in other countries.

On the ground in Ukraine, Russia kept up its push to capture the small eastern city of Bakhmut and secure its first substantial victory in more than half a year. Milley said Russia was making small advances near Bakhmut but at a great cost.

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Ukraine’s President Volodymyr Zelenskiy said his military top brass had advised reinforcing Bakhmut.

Kyiv had appeared last month to be preparing to pull out of the city but has since decided to defend it, saying it is exhausting Russia’s attacking force there to pave the way for its own counter-attack.