President Volodymyr Zelensky watched troops training with some of their new Western-supplied anti-tank weapons on a range near Rivne, west of the capital Kyiv.

Then he travelled to the frontline port city of Mariupol, and gave a speech to mark what he had declared Ukraine's "Day of Unity", wearing a military-style olive green coat and vowing resistance.

"We are not afraid of forecasts, we are not afraid of anyone, of any enemies," Zelensky said. "We will defend ourselves."

The demonstration of Ukrainian firepower and rhetoric contrasted with images on Russian state media that were said to show Moscow's forces bringing an end to a major exercise in occupied Crimea.

But Zelensky denied that this was a sign of a Russian pullback.

"We are seeing small rotations. I would not call these rotations the withdrawal of forces by Russia. We cannot say that," he said in televised comments, adding: "We see no change."

In Rivne, missiles pounded targets and armoured vehicles manoeuvred and fired on the yellowing moorland, while in Kyiv hundreds of civilians marched in a stadium with an enormous national banner.

The "Day of Unity" displays came as the Kremlin called for "serious negotiations" with Washington, and European leaders pushed hard for a diplomatic resolution to the crisis.

- 'New normal in Europe' -

But NATO chief Jens Stoltenberg, who hosted a meeting of the alliance's defence ministers in Brussels, dismissed suggestions that the threat on the border had diminished.

He said the alliance would shore up its eastern defences with forward deployments in member states bordering Ukraine.

"Moscow has made it clear that it is prepared to contest the fundamental principles that have underpinned our security for decades and to do so by using force," he said.

"I regret to say that this is the new normal in Europe."

And on reported Russian troop movements, he said: "So far we do not see any sign of de-escalation on the ground; no withdrawals of troops or equipment.

"Russia maintains a massive invasion force ready to attack with high-end capabilities from Crimea to Belarus."

British Prime Minister Boris Johnson agreed, saying there was "currently little evidence of Russia disengaging" from its military build-up.

Johnson and United Nations Secretary-General Antonio Guterres agreed during a call on Wednesday that any Russian invasion would have "catastrophic and far-reaching consequences," Downing Street said.

- US Navy aircraft intercepted -

Russia's huge build-up of troops, missiles and warships around Ukraine is being billed as Europe's worst security crisis since the Cold War.

Russian President Vladimir Putin has demanded Ukraine be forbidden from pursuing its ambition to join NATO and wants to redraw the security map of eastern Europe, rolling back Western influence.

But, backed by a threat of crippling US and EU economic sanctions, Western leaders are pushing for a negotiated settlement, and Moscow has signalled it will start to pull forces back.

In the latest such move, on Wednesday the Russian defence ministry said military drills in Crimea -- a Ukrainian region that Moscow annexed in 2014 -- had ended and that troops were returning to their garrisons.

Washington has demanded more verifiable evidence of de-escalation, but US President Joe Biden has nevertheless vowed to push for a diplomatic solution.

Kremlin spokesman Dmitry Peskov welcomed this, telling reporters: "It is positive that the US president is also noting his readiness to start serious negotiations."

Meanwhile the Pentagon said that three US Navy aircraft were intercepted by Russian planes in an "unprofessional" manner over the Mediterranean Sea last weekend.

"While no one was hurt, interactions such as these could result in miscalculations and mistakes that lead to more dangerous outcomes," US Navy Captain Mike Kafka said.

- US slams invasion 'pretext' -

The US State Department said Russia was attempting to create a "pretext" for invading with unsupported claims of "genocide" and mass graves in Ukraine's eastern Donbass region, which is controlled by Moscow-backed separatists.

"Over the past several weeks, we've also seen Russian officials and Russian media plant numerous stories in the press, any one of which could be elevated to serve as a pretext for an invasion," State Department Spokesman Ned Price said.

EU leaders, already gathered in Brussels for a summit with their African counterparts, are now to hold impromptu crisis talks on Russia and Ukraine on Thursday.

A UN Security Council meeting on Thursday is also set to discuss the crisis.

On Tuesday, Ukraine said the websites of the country's defence ministry and armed forces as well as private banks had been hit by a cyberattack of the kind that US intelligence fears would precede a Russian attack.

"It cannot be excluded that the aggressor is resorting to dirty tricks," Ukraine's communications watchdog said, in reference to Russia.

Peskov denied that Moscow had any role in the cyber assault.

"We do not know anything. As expected, Ukraine continues blaming Russia for everything," he said.

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