Baltic leaders said on Saturday they would back further sanctions against Russia at a European Union summit next week unless there was a de-escalation in eastern Ukraine where Kiev is trying to quell a pro-Russian insurgency.
Hours after the start of a ceasefire on Friday, separatists attacked Ukrainian posts on the border with Russia and a military base, and tried to storm an airforce base, Ukrainain security forces said.
Earlier on Friday, the leaders of the United States, France and Germany agreed Russia risks new sanctions if it fails to take immediate steps to defuse tensions on the Ukraine border.
Leaders of EU's member states may discuss the issue at a summit in Brussels next week.
Latvia, Lithuania and Estonia - which all broke away from the Soviet Union in 1990-1991 - had already called for tougher EU sanctions against Moscow after its annexation of Crimea.
"If there will be no de-escalation of the situation then Latvia will support a third bloc of sanctions," Latvian Prime Minister Laimdota Straujuma told a news conference after meeting with her Baltic counterparts and European Commission President Jose Manuel Barroso in the Estonian capital.
Lithuanian Prime Minister Algirdas Butkevicius said his position was the same, while their Estonian counterpart, Taavi Roivas, said that if there was no de-escalation in Ukraine, further sanctions would be the EU's only choice.
So far, the EU has imposed limited measures - asset freezes and travel bans on people and companies in Russiaand Ukraine - and has mulled steps against Russia including restrictions ranging from luxury goods imports to an oil and gas ban. There has been no consensus on how to proceed.
States with close trade and energy ties with Russia, such as Italy, Greece and Germany, worry about the potential impact on their economies of stricter sanctions while others, such as Cyprus and Austria, have close financial links.
Concerns over Europe's gas supplies are a major consideration in the decision around sanctions as EU consumers get about a third of their gas needs from Russia, around half of it through pipelines that cross Ukraine.
Barroso at the news conference urged EU member states to reach a common stance on the issue of further sanctions.
"I am pleading for a common position of the member states," he said. (Reporting by David Mardiste; Writing by Anna Ringstrom; Editing by Raissa Kasolowsky)