US President Joe Biden says there’s “every indication” Russia is preparing to invade neighbouring Ukraine in coming days and is creating an excuse to justify the attack.
Mr Biden said Moscow was engaging in a “false-flag operation” after Russian-backed separatists in eastern Ukraine accused government forces of opening fire on their territory.
Mr Biden said Russia was looking for an “excuse to go in”.
“Every indication we have is they’re prepared to go into Ukraine and attack Ukraine,” Mr Biden told reporters as he departed the White House.
“My sense is this will happen in the next several days.”
However Moscow has accused the US of stoking further tensions and reacted by expelling America’s second-most senior diplomat which the US said was another “escalatory” move.
Russia continues to deny Western accusations that it’s planning to invade its neighbour and said this week it was pulling back some of the 100,000 troops it has massed near the frontier.
Washington disputes there has been a significant withdrawal and said thousands more troops were still arriving.
Ukraine and pro-Russian rebels gave conflicting accounts of shelling across the front in the Donbass separatist region.
The details could not be established independently, but reports from both sides suggested an incident more serious than the routine ceasefire violations reported regularly in the area.
Mr Biden ordered Secretary of State Antony Blinken to change his travel plans at the last minute to speak at a United Nations Security Council meeting on Ukraine.
Mr Blinken told the council that Russia planned to manufacture a pretext for an invasion in coming days.
“This could be a violent event that Russia will bring on Ukraine, or an outrageous accusation that Russia will level against the Ukrainian government,” Mr Blinken said.
“It could be a fabricated so-called terrorist bombing inside Russia, the invented discovery of a mass grave, a staged drone strike against civilians, or a fake — even a real — attack using chemical weapons.
“Russia may describe this event as ethnic cleansing, or a genocide.”
British Foreign Secretary Liz Truss said the Russian government’s claims of abnormal activity by Ukrainian forces was an attempt to fabricate a reason for invasion.
“Reports of alleged abnormal military activity by Ukraine in Donbas are a blatant attempt by the Russian government to fabricate pretexts for invasion. This is straight out of the Kremlin playbook,” Ms Truss said on Twitter.
She said Britain would “continue to call out Russia’s disinformation campaign”.
NATO Secretary-General Jens Stoltenberg echoed the British foreign secretary’s comments.
“We are concerned that Russia is trying to stage a pretext for an armed attack against Ukraine, there is still no clarity, no certainty about the Russian intentions,” Mr Stoltenberg told reporters after a two-day meeting of NATO defence ministers at the alliance’s headquarters in Brussels.
Ukraine’s President Volodymyr Zelenskiy said pro-Russian forces in eastern Donbass region had shelled a kindergarten and this was a “big provocation”.
“It’s important that diplomats and the OSCE remain in, their monitoring activities are an additional deterrent. We need an effective mechanism for recording all ceasefire violations,” Mr Zelenskiy said on Twitter on Thursday.
Kremlin spokesperson Dmitry Peskov said Moscow was “seriously concerned” about the reports of an escalation.
Russia has long accused Kyiv of planning to provoke escalation as an excuse to seize rebel territory by force, which Ukraine denies.