<a href="https://www.thenationalnews.com/tags/russia/" target="_blank">Russia</a> has begun withdrawing its diplomatic staff from <a href="https://www.thenationalnews.com/tags/ukraine/" target="_blank">Ukraine</a>, the Russian state-owned Ria Novosti news agency reported on Saturday amid <a href="https://www.thenationalnews.com/world/us-news/2022/02/11/russian-invasion-of-ukraine-could-begin-any-time-us-says/" target="_blank">mounting fears</a> that Moscow will soon launch an invasion after months of military build-up on the borders with its neighbour. "Russian diplomats and consular officers in Ukraine have begun to leave for Russia," Ria Novosti quoted a source as saying. Russia has said it had no plans to invade Ukraine and has not officially announced the withdrawal of its diplomatic staff there, but the source said a reduction in personnel was indicated by the increased difficulty in obtaining appointments at Russia's embassy and consulates. Commenting on the reported withdrawal, Foreign Ministry spokeswoman Maria Zakharova said Russia had decided to "optimise" staffing at its missions in Ukraine in view of "possible provocations by the Kiev regime or third countries". However, they would continue to provide basic services, she wrote on her Telegram account. The US and a number of allies have called on their citizens to leave Ukraine after National Security Adviser Jake Sullivan <a href="https://www.thenationalnews.com/world/us-news/2022/02/11/russian-invasion-of-ukraine-could-begin-any-time-us-says/" target="_blank">said on Friday</a> a Russian invasion of Ukraine could come at “any time”. State Department officials told Associated Press that US embassy staff would be asked to leave Kiev on Saturday, but the decision was not officially confirmed. US President Joe Biden and Russian President Vladimir Putin are scheduled to speak by phone later on Saturday, White House and Kremlin officials said. US Secretary of State Antony Blinken said he would speak to Russian Foreign Minister Sergey Lavrov, and warned Washington and its allies would swiftly impose severe economic sanctions if Russia invaded Ukraine. "We continue to see very troubling signs of Russian escalation, including new forces arriving around Ukraine's borders," Mr Blinken said at a press conference in Fiji, where he attended a meeting of Pacific leaders. "If Russia is genuinely interested in resolving this crisis of its own making through diplomacy and dialogue, we're prepared to do that," he said. "But it must take place in the context of de-escalation. So far, we've only seen escalation from Moscow," he said. "This is a pivotal moment. We're prepared for whatever should happen." Mr Sullivan said on Friday a major Russian military operation could start rapidly. “We can’t pinpoint the day at this point, and we can’t pinpoint the hour, but that is a very, very distinct possibility,” Mr Sullivan said. “The strong possibility of action, the distinct possibility of action, in a relatively near-term time frame … is backed up by our view of what’s happening on the ground.”