Tornadoes and winds approaching 70mph are now forecast for the region - a day after the storm knocked out power to two million people in Russia and Ukraine.

At least 14 people were killed in the two countries, officials said, as trees came down and coastal areas were pounded by large waves.

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The Institute for the Study of War (ISW), based in Washington, said the weather had affected the "the tempo of military operations along the frontline" but hadn't stopped them entirely.

"The Ukrainian Navy and Ukraine's Southern Operational Command notably reported that dangerous weather in the Black Sea forced Russia to return all of its naval vessels and missile carriers to their base points," said the ISW.

"A prominent Russian milblogger warned that the threat of mines in the Black Sea will increase for both military and civilian vessels in the coming days because the storm has broken boom nets and dispersed minefields, causing mines to drift throughout the northwestern Black Sea."

It said "several sources" also reported rail lines had been damaged in coastal areas and that it could cause logistical problems for Russia in Crimea and southern Ukraine.

Crimea, annexed by Russia in 2014, is a vital military and logistics hub for President Vladimir Putin's forces.

Ukraine's President Volodymyr Zelenskyy said at least five people had been killed in the storm in the southern Odesa region and that work was going on to restore electricity to some villages.

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Almost 100,000 people were also still without power in Crimea on Tuesday morning and some people had no water supply, according to the region's Russia-installed governor.

A state of emergency is still in place in several areas there.

The storm also dumped 10 days' worth of snow - about 25cm - in the Vologda region, north of Moscow, in one day, according to Russia's Tass news agency.

Moscow itself was also covered in snow on Monday and blizzard-like conditions were seen in Moldova, Romania, Bulgaria and Serbia on Sunday.