Ukraine’s top security official Oleksiy Danilov says Ukraine will impose a state of emergency on all of its territory, apart from the Donetsk and Luhansk regions where it has been in place since 2014.
He said that the emergency state would last 30 days and could be extended for another 30 days.
Pro-Russian separatists have controlled parts of Donetsk and Luhansk since 2014.
Russia recognised them as independent states and approved use of its troops abroad this week.
The United States and its allies, including Australia, have accused Russia of flagrantly violating international law by ordering troops into the two separatist regions.
Mr Danilov also said that Ukraine’s President Volodymyr Zelenskiy had not discussed the development of nuclear weapons, something Vladimir Putin has said posed a strategic threat for Russia.
Meanwhile, Russia’s FSB security service says it has foiled “an act of terrorism” in annexed Crimea and arrested six Russian citizens it says are supporters of a Ukrainian extremist group, the RIA news agency reports.
The FSB said it had also seized components for making explosive devices, RIA reported.
Moscow annexed Crimea from Ukraine in 2014.
The FSB was expected to publish more details later on Wednesday.
The US and its allies sought to step up sanctions pressure on Russia on Wednesday over the deployment of troops in separatist regions of eastern Ukraine, in one of the worst security crises in Europe in decades.
It comes as Pope Francis says the threat of war in Ukraine causes “great pain in my heart” and he’s condemned actions “destabilising coexistence among nations and discrediting international law”.
Pope Francis, speaking in a sombre tone at the end of his weekly general audience, also urged politicians to make “a serious examination of conscience before God” about the effects of their actions.
He proclaimed Ash Wednesday, on March 2 this year, as an international day of fasting and prayer for peace.
He condemned the “diabolic senselessness of violence” and asked the Madonna, “the queen of peace, to save the world from the madness of war”.
“I have great pain in my heart because of the worsening of the situation in Ukraine,” Francis said, adding that he was anguished and worried like many around the world because peace was threatened by partisan interests.
“I appeal to all sides to abstain from any action that could provoke more suffering to the populations, destabilising coexistence among nations and discrediting international law.”
The United States, the European Union, Britain, Australia, Canada and Japan announced plans to target banks and elites while Germany halted a major gas pipeline project from Russia in one of the worst security crises in Europe in decades.
It was the second time Francis has called an international day of prayer for peace in Ukraine. The first was on January 26.