BERLIN: Germany on Saturday advised German citizens without an "imperative" reason to stay in Ukraine to leave, saying a "military conflict cannot be excluded" after Washington warned a Russian invasion could begin "any day".

"Tensions between Russia and Ukraine have again shot up in the last few days due to the massive movements of Russian military units near the Ukrainian border," the German foreign ministry said.

"If you are currently in Ukraine, make sure that your presence is imperative. If that is not the case, please leave the country for the time being".

Biden to sound out Putin as US warns of Ukraine war 'any day'

Germany also said it was reducing its diplomatic representation in Ukraine. "We will keep our embassy open in Kyiv but reduce diplomatic staff," said Foreign Minister Annalena Baerbock during a visit to Egypt.

Belgium and the Netherlands joined Germany in becoming the latest Western countries to advise their citizens to leave Ukraine. Russia also announced that it had withdrawn some diplomatic staff fearing "provocations" from the West or Kyiv.

The US embassy in Kyiv on Saturday ordered the evacuation of non-emergency staff.

Russian leader Vladimir Putin was due to talk to US President Joe Biden and France's Emmanuel Macron by telephone later on Saturday.