Russia said more of its forces surrounding Ukraine were withdrawing on Wednesday, but Nato urged Moscow to prove it was pulling back, saying there were signs that more troops were on the way.
Britain joined the United States in saying it had yet to be convinced the pullout was real, while in Ukraine, the defence ministry said an unprecedented cyberattack was into its second day. Russia said it had nothing to do with any attack.
The Russian defence ministry published video that it said showed tanks, infantry fighting vehicles and self-propelled artillery units leaving the Crimean Peninsula, which Moscow seized from Ukraine in 2014.
Nato secretary-general Jens Stoltenberg said a pullout would be welcome but that moving troops about did not confirm it.
"It remains to be seen whether there is a Russian withdrawal ... What we see is that they have increased the number of troops, and more troops are on the way," he told reporters at the start of a two-day meeting of Nato defence ministers at the alliance's headquarters in Brussels.
The deployment in the Crimean Peninsula was part of a huge build-up of Russian forces to the north, east and south of Ukraine since November that had prompted London and Washington to warn in recent days that a Russian invasion looked imminent.
Russia mocked those warnings as hysterical war propaganda when it announced on Tuesday that some units were starting to return to base after completing exercises.
On Wednesday the Kremlin said Nato was wrong to say there was no evidence of a pullout and that Putin had stressed his desire to negotiate.
Military analysts say a key indicator of a significant pullback will be whether units from Russia's far east, which are taking part in huge exercises in Belarus this week, return to their bases thousands of miles away.
US president Joe Biden said on Tuesday that more than 150,000 Russian troops were still amassed near Ukraine's borders. He said Washington had not yet verified any pullout.
"Our analysts indicate that they remain very much in a threatening position," he said.
British Defence Secretary Ben Wallace told Times Radio on Wednesday: "We haven't seen any evidence at the moment of that withdrawal."
Speaking separately to the BBC, he said: "Physical observations that we see show the opposite of some of the recent rhetoric coming out the Kremlin."
Hacking attack
In Ukraine, people raised national flags and played the country's anthem to show unity against fears of an invasion.
The defence ministry said hackers were still bombarding its website and had succeeded in finding vulnerabilities in the programming code.
Although Kyiv did not name who was behind the incident, a statement suggested it was pointing the finger at Russia.
"It is not ruled out that the aggressor used tactics of dirty little tricks because its aggressive plans are not working out on a large scale," said the Ukrainian Centre for Strategic Communications and Information Security, which is part of the culture ministry.
Russia's Federal Security Service did not immediately reply to a request for comment from Reuters.
"If Russia attacks the United States or our allies through asymmetric means like disruptive cyberattacks against our companies or critical infrastructure, we're prepared to respond," Biden said in televised remarks from the White House on Tuesday.
Russia has always denied planning to invade Ukraine but has been pressing for a set of security guarantees from the West including a promise that its neighbour Ukraine will never join Nato.
The United States and its allies have rejected that, but say they are willing to talk about arms control and confidence-building measures.
Putin said after meeting German chancellor Olaf Scholz on Tuesday that the West was ignoring Russia's main demands, but Moscow was ready to continue dialogue on security issues.
European Union Council head Charles Michel urged Russia on Wednesday to take tangible steps to de-escalate.
"The choice today is a choice between war and tragic sacrifices that would go along with that war or the courage of a political engagement, the courage of a diplomatic negotiation", he said. - Reuters
