A “significant escalation” by Russian forces in Ukraine, as fears mount over Moscow’s intentions, leads many of the national papers.

The Sun says 35 people were killed when Russia struck a Ukrainian military base close to Nato-member Poland’s border, in a story also covered by The Independent.

The strike prompted a warning from the European-American alliance and was cast as a “significant escalation” by the UK, according to The Guardian.

The i picks up the story and reports the move means Vladimir Putin has brought “war to door of Nato”, in a line echoed by the Daily Express and The Times.

The Daily Telegraph quotes Cabinet minister Michael Gove as saying the Russian leader was “pushing the boundaries” of warfare.

The Financial Times and the Daily Mail say the strike has sent a warning signal to Nato amid fears the invasion could spread beyond Ukraine, with the Daily Mirror reporting Mr Putin has “the West in his sights”.

Metro reports Britons have been urged to open their homes to people fleeing the war.

And the Daily Star cites “the world’s top spy network” as saying Mr Putin invaded Ukraine because he is “pumped up on steroids”.