“Washington’s efforts have created all the prerequisites for Ukraine to lose its sovereignty and lose part of its territories,” Patrushev said.

Ukraine said on Thursday that it had installed a military commandant in the area it controlled, even as Russia intensified its offensives in Ukraine’s east.

Russia’s defence ministry for its part said it had repelled a series of Ukrainian attacks along the Kursk frontline.

Kursk regional governor Alexei Smirnov said Ukraine had destroyed a road bridge over the Seym river in the region’s Glushkovsky district. State news agency TASS, citing Russian security officials, said that could hinder an ongoing evacuation of the frontier district’s roughly 20,000 inhabitants.

While the Ukrainian attack has revealed weaknesses in Russian defences and changed the public narrative of the conflict, Russian officials said Ukraine’s “terrorist invasion” would not change the course of the war.

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Russia has been advancing for most of the year in the key eastern sector of the 1000-km front and has vast numerical superiority. It controls 18 per cent of Ukraine.

After more than 10 days of fighting, Ukraine holds at least 450 sq km of territory. But for Putin, the incursion crosses another red line.

One Russian source told Reuters the incursion could embolden hardliners in Moscow who advocate a bigger war, but Putin’s choice may not be easy.

He has sought to portray Europe’s biggest war in seven decades both as a limited “special military operation” that need not upset daily Russian life and as a historic fight with a West that scorns Moscow’s interests and seeks to dismember Russia.

The US, which has said it cannot allow Putin to win the Ukraine war, so far deems the surprise incursion a protective move that justifies the use of US weaponry, officials in Washington said.

But they also expressed worries about complications as Ukrainian troops push further into enemy territory.

One US official, speaking on condition of anonymity, said that if Ukraine started taking Russian villages and other non-military targets using US weapons and vehicles, it could be seen as stretching the limits Washington has imposed, precisely to avoid any perception of a direct NATO-Russia conflict.

Russia’s defence ministry has published footage that it said showed a Russian drone destroying a US-made Stryker armoured combat vehicle in the Kursk region.

Kyiv’s allies are largely withholding judgment over the Ukrainian offensive into Russian territory amid uncertainty over the ultimate goal of an operation that’s sought to redraw the map of the Kremlin’s 2 1/2-year war.

Several NATO allies have backed Ukraine’s decision to send troops into the western Kursk region.

But some have voiced misgivings publicly and privately, citing the risk that the escalation in fighting could divert badly needed troops from a fragile front line and potentially sow division among Kyiv’s backers, according to Western officials who spoke on condition of anonymity.

Reuters, Bloomberg