Western allies on Thursday rejected Russia's bid to thwart Kiev's Nato ambitions and urged Moscow to stop its military build-up along Ukraine's border and return to talks led by France and Germany.
EU leaders, meeting in Brussels, insisted on "the urgent need for Russia to de-escalate tensions caused by the military build-up along its border with Ukraine and aggressive rhetoric".
They repeated a threat to impose "massive consequences and severe cost" on Moscow through sanctions, co-ordinated with the EU's partners in London and Washington.
The US has used similar language of retaliation in the event of a Russian invasion, while trying to speak with Moscow to defuse the situation.
Nato Secretary General Jens Stoltenberg called Russia the "aggressor".
Russian President Vladimir Putin wants direct dialogue with US leader Joe Biden to resolve the stand-off, and is seeking security guarantees to stand down his troops.
But the European leaders in their summit pushed for a return to the "Normandy format", a four-way dialogue between Paris, Berlin, Kiev and Moscow.
On Wednesday, Russia handed a list of security demands to US assistant secretary of state Karen Donfried, who then went to Nato headquarters in Brussels to discuss them with Mr Stoltenberg.
The Nato chief also met Ukraine's President Volodymyr Zelenskiy. The two insisted that any decision on membership was a matter for Kiev and the alliance's 30 member states.
"We will not compromise on the right of Ukraine to choose its own path," Mr Stoltenberg said. "We will not compromise on the right for Nato to protect and defend all Nato allies."
He said there would also be no compromising on Nato's partnership with Ukraine, calling it important for both sides and "not in any way a threat to Russia".
On Wednesday, Mr Zelenskiy attended a summit with EU leaders, most of whose countries are also Nato members, and said the majority of them supported Ukraine's position in the conflict.
But he is frustrated that European powers in particular have refused to take preventive action against Russia, instead issuing threats in the event of action.
"Since 2014, since the start of the war, I believe that basically Russia pushed Ukraine into Nato," Mr Zelenskiy said. "Basically I believe that today Russia itself is paving the difficult path of Ukraine to Nato."
He said that, in his view, some EU members did not seem to understand the extent of Ukraine's peril and urged them to act swiftly.
On Wednesday, Russia's deputy foreign minister Sergei Ryabkov told Ms Donfried that Nato should halt its eastward expansion and withdraw a promise that Ukraine could become a candidate for membership.
The US said Ms Donfied would stress "we can make diplomatic progress on ending the conflict in the Donbas through implementation of the Minsk agreements in support of the Normandy Format".
Ukraine and its closest supporters in the West want to cancel the opening of the Nord Stream 2 pipeline, which will carry Russian gas supplies to Germany, bypassing Ukraine.
Germany's new leader, Chancellor Olaf Scholz, has been cautious on this point, and some of the leaders meeting in Brussels fear pre-emptive sanctions would provoke rather than deter Russia.
Getting Russia back to the negotiating table will not be easy.
"Moscow does not want to return to the Normandy format and wants to negotiate with the United States," a senior European diplomat said.
The diplomatic track was established at a summit in Minsk in 2015 where Mr Putin accepted that France and Germany should be moderators in the talks between the two.
"The Americans support a return to this format, and talks are under way with Moscow but nothing has been agreed yet," the European envoy said.