Ukraine's parliament has adopted a statement branding Russia an "aggressor state," a move that deputies hope will pave the way for punishment under international law.
The Verkhovna Rada also voted on January 27 to define separatist self-styled "people's republics" in the eastern regions of Donetsk and Luhansk as "terrorist organizations," and to appeal to the international community for additional nonlethal military aid and stronger sanctions against Russia.
Radical Party leader Oleh Lyashko, a member of the governing coalition, said, "Legal recognition as an aggressor state entails consequences" under the UN Charter and UN resolutions.
In reaction, Russian Deputy Foreign Minister Grigory Karasin called the Ukrainian statement "thoughtless and irresponsible," and said it was aimed at blocking efforts to end the conflict between government forces and pro-Russian rebels that has killed more than 5,000 people in eastern Ukraine since April.
Earlier on January 27, European Union leaders called on their foreign ministers to consider an appropriate response to the escalation of fighting in eastern Ukraine, including possible new sanctions, at their January 29 meeting in Brussels.
"In view of the worsening situation we ask the upcoming Foreign Affairs Council to assess the situation and to consider any appropriate action, in particular on further restrictive measures, aiming at a swift and comprehensive implementation of Minsk agreements," the leaders said in a statement.
The 28-member bloc has imposed a series of economic and political sanctions on Russia and officials linked with Russia's illegal annexation of Crimea last March and its support for separatists fighting government forces in eastern Ukraine.
The EU leaders' statement noted in "evidence of continued and growing support given to the separatists by Russia" and said that support "underlines Russia’s responsibility."
The statement also urged Russia to condemn separatists' actions and to implement the September 2014 Minsk agreements, which include a cease-fire deal.
The EU leaders also condemned the killing of 30 civilians on January 24 through "the indiscriminate shelling of the Ukrainian city of Mariupol."
The United Nations said rockets fired from separatist-controlled territory into a residential neighborhood of Mariupol deliberately targeted civilians in an attack that violated international humanitarian law.
The shelling reignited fears the separatists would seek to seize the Azov Sea port city and push further toward the Black Sea peninsula of Crimea.
The Mariupol attack came a day after a separatist leader said rebels would try to take more territory and would no longer seek peace talks with Kyiv.
Despite that, Russia has blamed Kyiv for the escalation of fighting.
The Kremlin said that in telephone conversations with German Chancellor Angela Merkel and French President Francois Hollande late on January 26, Putin said the cause of the escalation was "the Kyiv authorities' policy of subduing the Donbas by force."
Donbas is a term for the industrial portion of eastern Ukraine where the separatists hold parts of the Donetsk and Luhansk provinces, including their capitals.
The Kremlin said Putin told Merkel and Hollande that he had sent a letter to Ukrainian President Poroshenko on January 15 proposing a withdrawal of heavy weapons from the front lines, but that there was no formal response until January 26 and in the meantime "large-scale combat actions were launched."
Western governments have said Putin's proposal was an attempt to seize more territory and avoid commitments Russia signed on to in the cease-fire deal agreed in Minsk in September.
Meanwhile, Ukrainian military spokesman Vladyslav Seleznyov said on January 27 that nine government soldiers were killed and 29 wounded by fighting in eastern Ukraine during the previous 24 hours.
Seleznyov told a briefing in Kyiv, "The situation remains tense. In the past 24 hours illegal armed groups carried out 120 attacks on government positions."
He said that the fighting was the most intense near the strategic town of Debaltseve, located northeast of rebel-held Donetsk.
The pro-Russian separatists have been attempting to encircle the government-controlled Debaltseve, which straddles key transport routes between the two rebel strongholds of Donetsk and Luhansk.