NATO Secretary-General Jens Stoltenberg has called on Russia to end "political, military and financial support for separatists" fighting Kiev troops in Ukraine, after a summit that saw the alliance boost its eastern flank to counter Moscow.
NATO agreed to deploy four battalions in Poland, Lithuania, Latvia and Estonia, former communist states that are now members of the alliance but have grown increasingly wary of Russia since it annexed Crimea in 2014 and backed Russian-speaking rebels in Ukraine's industrial east.
"Allies are united in their support for Ukraine's sovereignty and territorial integrity," Mr Stoltenberg told a joint news conference with Ukrainian President Petro Poroshenko on Saturday.
"We do not and we will not recognise Russia's illegal and illegitimate annexation of Crimea and we condemn Russia's deliberate destabilisation of eastern Ukraine, where ceasefire violations occur on daily basis."
The truce in east Ukraine is patchy and implementation of a broader peace plan - negotiated in Minsk between Ukraine and Russia by Germany and France - has been stalled for months.
"We call on Moscow to end its political, military and financial support for the separatists. All parties must fully implement the Minsk agreements," Mr Stoltenberg said.
Berlin and Paris have renewed a diplomatic push in recent weeks to implement Minsk in full, which means Kiev must grant special legal status to the rebel-held east and decentralise the country in a constitutional reform.
Moscow is obliged to help Kiev regain control of Ukraine's eastern border.
But some in the West - both NATO and the European Union - are increasingly bothered with what they see as Ukraine's slow progress on economic reforms and efforts to stamp out grass-root corruption and are pushing to restart dialogue with Russia after two years of relative isolation and sanctions against Moscow.