Nato has said Moscow will have no say in whether Ukraine joins the alliance, rejecting Russia's push for a de facto veto on its neighbour's security arrangements and urging it to reverse a build-up of military forces near their shared border.
Russian president Vladimir Putin has told western leaders that he wants binding guarantees that Nato will not allow Ukraine to become a member and will not station missiles on its territory.
Moscow handed proposals on the issue to a visiting senior US diplomat this week and said it was ready to start talks on the matter immediately, while continuing to move troops and armour towards Ukraine in what Kiev and its allies fear could be preparations for an all-out invasion.
Nato secretary general Jens Stoltenberg held talks with Ukrainian president Volodymyr Zelenskiy on Thursday, and said Russia now had "tens of thousands of combat-ready troops, tanks, artillery, armoured units, drones, electronic warfare systems" within striking distance of Ukraine.
"We see no sign that this build-up is stopping or slowing down ... it has no justification, it is provocative, destabilising and undermines security in Europe. We call on Russia to return to diplomacy, to de-escalate and respect Ukraine's sovereignty and territorial integrity," he added.
Ready to talk
Mr Stoltenberg said he wanted to “send a very clear message that we can and are ready to talk to Russia ... We believe that dialogue is important especially when times are difficult”, but insisted that the alliance would not rule out membership for Ukraine or any other state to satisfy the Kremlin.
“Nato has an open-door policy. This is enshrined in Nato’s founding treaty ... The message today to Russia is that it is for Ukraine as a sovereign nation to decide its own path. And for the 30 Nato allies to decide when Ukraine is ready to become a member.”
Mr Zelenskiy said that in the event of all-out war with Russia, Ukraine would effectively be “an outpost” defending Nato member states in Europe, without being a member itself.
He also said Russia had forced his country to seek Nato protection by occupying Crimea in 2014 and launching a proxy war in eastern Ukraine between Moscow-led separatists and government troops, which has claimed 14,000 lives.
“I believe that Russia has pushed Ukraine into Nato. I believe that today Russia is ‘paving’ Ukraine’s difficult way to Nato,” Mr Zelenskiy said.
Russia denies planning an all-out invasion of its neighbour, but also warns of a “military response” if the West fails to respect its “red lines” regarding Ukraine and its push for binding security guarantees.
Ukrainian foreign minister Dmytro Kuleba said the only thing missing from Thursday's "very good, positive" talks in Brussels was an announcement of "when Ukraine will become a Nato member – they didn't tell us, though we asked".