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Mr Stoltenberg said Russia’s public statements could not be trusted as he became the latest western official to play down Moscow’s claim that it would scale back operations around the Ukrainian capital.
He said Russia planned to use some of its relocated forces to strengthen its offensive in the eastern Donbas region where it supports pro-Kremlin separatists in a long-running conflict with Ukrainian forces.
“According to our intelligence, Russian units are not withdrawing, but repositioning,” Mr Stoltenberg said at the launch of a Nato annual report on Thursday.
“At the same time, Russia maintains pressure on Kyiv and other cities, so we can expect additional offensive actions bringing even more suffering,” he said.
British military intelligence offered a similar assessment, saying a few Russian units had withdrawn from near Kyiv but that invading forces still held positions on either side of the city.
Heavy fighting is expected to continue in Kyiv’s suburbs in the coming days, said Britain’s Defence Ministry, which said Russian shelling and missile strikes had continued in Chernihiv despite a similar promise to reduce attacks there.
Five weeks into the war, western officials believe Russia has made faltering progress but is turning to the mercenary Wagner Group to shore up its forces and absorb some of its military losses.
Ukrainian President Volodymyr Zelenskyy said in an address to the Dutch parliament on Thursday that news of bombings and missile strikes was starting to become routine as fighting continues with no obvious breakthroughs.
Nonetheless, President Vladimir Putin is not willing to support a ceasefire because he believes the conditions are not yet right, Italian Prime Minister Mario Draghi said on Thursday after a conversation with the Russian leader.
Mr Draghi echoed German Chancellor Olaf Scholz in saying he had extracted a promise from Mr Putin that European countries could still pay for gas imports in euros or dollars, rather than roubles as Moscow has been demanding.
The request for roubles is regarded by western powers as a way of evading the sanctions imposed by many Nato and other allied countries since Russia invaded Ukraine.
Mr Stoltenberg, who has spoken of the need for a rethink of Nato’s defence posture on its eastern flank, said the alliance’s security environment had “dramatically worsened” as a result of the Russian offensive.
The 154-page annual report said Mr Putin’s actions made clear that “his objectives are not limited to Ukraine”, as several Nato countries move to increase defence spending to face a newly hostile Russia.
Italy will reach the Nato target of spending 2 per cent of gross domestic product on its military in 2028, Mr Draghi said on Thursday. But he said there would be no increase spelled out in an upcoming economic forecast.
Latvia this week signed off plans to increase defence spending to 2.5 per cent, while Germany, Denmark and Norway have all promised to raise their military budgets. The annual report showed Nato's overall spending rising for the seventh consecutive year.
Nato countries have ruled out sending troops beyond the alliance’s borders and intervening directly in Ukraine, for fear of provoking Russia into a wider European war.
Accepting that, Mr Zelenskyy is pushing for tougher sanctions on Russia and on Thursday called for sea ports to be closed to the country’s ships after the closure of Europe’s airspace to its planes.
General Sir Nick Parker, a former commander of UK land forces who has advised Ukraine’s Defence Ministry, said Nato had adopted a defensive position by putting a protective ring around its members but not being prepared to develop an “offensive counter-strategy to Putin”.
“Slightly controversially I suppose, I mean Nato’s been defeated, Nato’s bluff was called,” he told BBC Radio 4’s Today programme.
Mr Zelenskyy said in his speech to Dutch MPs that Ukraine needed shells, missiles, air defences and anti-tank weapons to fight off the Russian attacks.
In a separate address he said that Russian forces were building up in the Donbas and that new strikes were expected on the region.