In a statement, the Foreign and Commonwealth Office stressed that the British embassy in Kyiv "remains open and will continue to carry out essential work".

Sky News understands the staff being withdrawn are non-essential and the embassy remains fully operational.

It comes as Ireland's foreign minister Simon Coveney said Russian naval exercises in international waters in the Irish Sea are "not welcome".

Russia said late last week its navy would stage a sweeping set of exercises involving all its fleets from the Pacific to the Atlantic, the latest show of strength in a surge of military activity during a standoff with the West.

Mr Coveney said on Monday: "We don't have a power to prevent this happening but certainly I have made it clear to the Russian ambassador in Ireland that this is not welcome. This isn't a time to increase military activity and tension."

Hours before the UK withdrew some embassy staff and dependants, the US ordered the families of all American embassy staff in the capital to leave Ukraine amid heightened fears of a Russian invasion.

Read more: What's going on at the Russia-Ukraine border and where is Moscow hiding its tanks and missiles?

The US State Department told the dependants of staffers at the US embassy in Ukraine's capital that they must leave the country and said that non-essential employees could also leave at government expense.

US officials also stressed the Kyiv embassy will remain open and that the announcement does not constitute an evacuation.

The decision had been under consideration for some time and does not reflect an easing of US support for Ukraine, the officials added.

Ukraine's foreign affairs spokesperson Oleg Nikolenko has said the US decision is "premature" and one of "excessive caution".

Mr Nikolenko posted on Twitter: "We have taken note of @StateDept's decision re departure of family members of @USEmbassyKyiv staff.

"While we respect right of foreign nations to ensure safety & security of their diplomatic missions, we believe such a step to be a premature one & an instance of excessive caution."

The move comes amid rising tensions about Russia's military buildup on the Ukraine border that were not eased during talks between US Secretary of State Antony Blinken and Russian Foreign Minister Sergei Lavrov on Friday.

In a statement, the State Department noted recent reports that Russia was planning significant military action against Ukraine.

However, the Russian Foreign Ministry has accused NATO countries of escalating tensions around Ukraine with disinformation.

What's going on at the Russia-Ukraine border?

People told not to travel to Ukraine and Russia

US citizens have also been advised not to travel to the country due to the "increased threats of Russian military action and COVID-19", the US State Department said.

"The security conditions, particularly along Ukraine's borders, in Russia-occupied Crimea, and in Russia-controlled eastern Ukraine, are unpredictable and can deteriorate with little notice," it added.

"Demonstrations, which have turned violent at times, regularly occur throughout Ukraine, including in Kyiv."

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The department has requested all US citizens currently in the country complete an online form so it "may better communicate" with them if needed.

"This is especially important if you plan to remain in Ukraine," it said.

The State Department has also advised US citizens not to travel to Russia, adding that they are "strongly advised against traveling by land from Russia to Ukraine through this region".