NATO leaders are preparing a ‘positive message’ to give to Ukraine, but Russia has warned against any escalation of the war (Picture: AP/Reuters)

Russia has warned of ‘catastrophic consequences’ for Europe if the war in Ukraine in escalated.

NATO leaders are preparing to deliver a ‘positive message’ to Kyiv over its future prospects for joining the military alliance.

But the Kremlin said NATO’s eastern expansion was a key factor in its decision to invade Ukraine 17 months ago, and if Ukraine were to join the alliance, Moscow would react clearly and firmly.

Konstantin Gavrilov, a Vienna-based senior Russian security negotiator, accused the United States of fuelling the conflict by pouring arms into Ukraine ahead of the NATO summit.

He said Europe would be the first to face ‘catastrophic consequences’ if the war escalated – but he did not say what these consequences would be.

Gavrilov also accused the United States of seeking to ‘undermine’ Russia.

He said: ‘Let’s look at the facts – the fate of Europe is of little interest to the United States.’

Earlier, Russia’s ambassador to the United States, Anatoly Antonov, made a similar criticism of what he called Washington’s ‘anti-Russian’ stance at the summit in Vilnius.

Anatoly Antonov, Russian ambassador to the United States, criticised Washington’s ‘anti-Russian’ stance (Picture: AP)

NATO leaders are set to approve the alliance’s first comprehensive plans since the end of the Cold War to defend against any attack by Moscow at the summit (Picture: AP)

‘Everything is being done to prepare local public opinion for the approval of any anti-Russian decisions that will be made in Vilnius in the coming days,’ Antonov said in a post on the embassy’s Telegram channel.

NATO leaders are set to approve the alliance’s first comprehensive plans since the end of the Cold War to defend against any attack by Moscow at the summit in Lithuania.

Russia’s ambassador to Belgium, Alexander Tokovinin, in comments cited by RIA, said those plans would make NATO’s confrontation with Moscow more tense and prolonged.

Russia did not detail what the consequences would be (Picture: Reuters)

Diplomats said differences were narrowing among the allies over Ukraine’s push for NATO membership, though it will not be invited to join the alliance while the war still rages.

‘Both the United States and NATO understand that time is not working for them. They are losing in Ukraine,’Gavrilov said.

Kyiv’s counteroffensive, which began last month, has been proceeding more slowly than hoped, but Ukraine’s military said on Monday its forces had caught occupying Russian troops ‘in a trap’ in the shattered eastern city of Bakhmut.

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Russia did not detail what the consequences would be.