US steps up invasion warnings as Ukraine tensions soar

Russian forces are taking part in joint military exercises with the military in Ukraine's neighbour Belarus

The United States stepped up warnings of an imminent Russian invasion of Ukraine on Thursday, despite Moscow's continued denials and announcements of troop withdrawals from near the border.

Adding to the already fierce tensions, Ukraine and Moscow-backed separatists traded accusations of intensifying shell fire across their frontline, with Western officials saying Moscow was looking to create a pretext for an invasion.

"Every indication we have is that they're prepared to go into Ukraine," he said, accusing Moscow of preparing a "false flag operation" as a pretext to invade.

At the United Nations, where the Security Council was set for a heated meeting on the crisis, the US envoy said Washington wanted to make clear that risk of a war in Europe was growing.

- 'Forced to respond' -

"In the absence of will on the American side to negotiate firm and legally binding guarantees on our security from the United States and its allies, Russia will be forced to respond, including with military-technical measures," the foreign ministry said.

Russia also expelled the number two US diplomat in Moscow, the US State Department said, condemning what it called an "unprovoked" action.

The Ukrainian army accused Russian-backed separatists of 34 ceasefire breaches on Thursday, 28 of them using heavy weapons.

"The shelling of a kindergarten... by pro-Russian forces is a big provocation," President Volodymyr Zelensky said on Twitter.

- 'Troubling' escalation -

The United States has claimed Moscow could be looking for a pretext to invade and earlier this week Russian President Vladimir Putin claimed that Kyiv was committing "genocide" in the eastern Donbas region.

"We've said for some time that the Russians might do something like this in order to justify a military conflict. So we'll be watching this very closely," Austin told journalists after a meeting with NATO counterparts. 

"Russia can still take the path of diplomacy. They can de-escalate, they can move their troops away from the border," she said.

Western officials say Russia has amassed well over 100,000 troops and significant military hardware near Ukraine's borders in preparation for a potential invasion.

Moscow has made several announcements of troop withdrawals this week and on Thursday said that units of the southern and western military districts, including tank units, had begun returning to their bases from near Ukraine.

After previously announced withdrawals earlier this week, the United States, NATO and Ukraine all said they had seen no evidence of a pullback, with Washington saying Russia had in fact moved 7,000 more troops near the border.

Putin has demanded that Ukraine be forever banned from fulfilling its hopes of joining NATO and for the alliance to roll back its deployments near Russia's borders.

"We have no need for soldiers with foreign flags on our territory. We are not asking for that. Otherwise, the entire world would be destabilised," he told the RBK Ukraine website.

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