A 30-day state of emergency has been declared in Ukraine in light of a feared invasion by Russia in the country's east, the secretary of the country's security council said on Wednesday.
The move could mean Ukrainians will be ordered to stay home or placed under curfew, Oleksiy Danilov said.
The move comes in response to Russia's decision to recognize two separatist regions in eastern Ukraine as independent countries and authorize Russian military forces to enter to prevent what the Kremlin insists is attempted genocide against ethnic Russians there.
The Ukrainian Foreign Ministry on Wednesday urged citizens living in Russia to leave that country "immediately." According to estimates, about 3 million Ukrainians reside in Russia. Many have family in both countries.
The West has responded to Russia's actions vis-a-vis Ukraine with a flurry of sanctions for what it calls a violation of international norms.
Britain announced sanctions against Russian oligarchs and banks, while Washington announced moves against Russian financial institutions and sovereign debt. The European Union announced its own package of measures.
The US and European countries have been warning for weeks that Russia is preparing an invasion, with more than 100,000 troops amassing on the Russian side of the joint border and - more recently - Russia's refusal to withdraw troops stationed in Belarus for military drills.
Russia responded that it was seeking guarantees that NATO forces would no longer operate forces in Eastern Europe - even in NATO member countries - and that Ukrainian NATO membership would be permanently off the table.
Russian President Vladimir Putin slammed the West on Wednesday for failing to respond to these demands, which he called "non-negotiable."
"Our country is always open for direct and open dialogue, for the quest for diplomatic solutions to difficult problems," he said in a video message released to mark Defence of the Fatherland Day, a day set aside to honour the armed services.
"But I repeat: The interests of Russia and the security of our citizens are non-negotiable for us," he said.
Putin has repeatedly indicated that he thinks NATO's eastward expansion is a threat to Russia.
"Today, securing the ability of our country's defence forces remains the most important duty of the state," he said.
Also on Tuesday, a debate about whether the Kremlin-backed TV station RT will be allowed to continue broadcasting in Britain was gathering pace.
Foreign Secretary Liz Truss has said it is up to Britain's communications regulator Ofcom whether the broadcaster would be allowed to continues with its licence, in comments reported by the Press Association.
"I think it is certainly true that (RT) is spouting propaganda on behalf of the Kremlin. One of the things the Kremlin does is use disinformation to try and sow discord in the West, and Russia Today is clearly part of that," she said.
Labour leader Sir Keir Starmer also called for action to tackle the "propaganda" put out by the channel, describing it as part of Putin's "campaign of misinformation."
