Russia could invade Ukraine "at any time" and American citizens should leave immediately, the US has warned.
An invasion could start with aerial bombing that would make departures difficult and endanger civilians, the BBC quoted the White House as saying on Friday.
Moscow has repeatedly denied any plans to invade Ukraine despite massing more than 100,000 troops near the border.
The US statement prompted countries around the world to issue fresh warnings to nationals in Ukraine, the report said.
The UK, Australia, Canada and the Netherlands are among those urging citizens to leave as soon as possible.
However, attempts to de-escalate tensions through diplomacy are set to continue on Saturday, with both US President Joe Biden and France's Emmanuel Macron due to speak to Russia's Vladimir Putin by phone.
Moscow, meanwhile, has accused Western countries of stirring up hysteria.
US National Security Adviser Jake Sullivan said Russian forces were now "in a position to be able to mount a major military action" in remarks seen as a clear escalation in the urgency of warnings from US officials, the BBC reported.
"We obviously cannot predict the future, we don't know exactly what is going to happen, but the risk is now high enough and the threat is now immediate enough that (leaving) is prudent," he said.
Sullivan added that the administration did not know if Putin had made a final decision to invade, but said that the Kremlin was looking for a pretext to justify military action, which he said could start with intense aerial bombardment.
(Only the headline and picture of this report may have been reworked by the Business Standard staff; the rest of the content is auto-generated from a syndicated feed.)
Dear Reader,
Business Standard has always strived hard to provide up-to-date information and commentary on developments that are of interest to you and have wider political and economic implications for the country and the world. Your encouragement and constant feedback on how to improve our offering have only made our resolve and commitment to these ideals stronger. Even during these difficult times arising out of Covid-19, we continue to remain committed to keeping you informed and updated with credible news, authoritative views and incisive commentary on topical issues of relevance.
We, however, have a request.
As we battle the economic impact of the pandemic, we need your support even more, so that we can continue to offer you more quality content. Our subscription model has seen an encouraging response from many of you, who have subscribed to our online content. More subscription to our online content can only help us achieve the goals of offering you even better and more relevant content. We believe in free, fair and credible journalism. Your support through more subscriptions can help us practise the journalism to which we are committed.
Support quality journalism and subscribe to Business Standard.
Digital Editor
RECOMMENDED FOR YOU