EU leaders on Thursday will call on Russia to stop its bombing in Syria and allow humanitarian aid to enter the besieged city in Aleppo.
Meeting in Brussels over the next two days, heads of state and government will also refuse to rule out sanctions against Moscow.
“We must show that robust and united European stance in the face of Russian aggression,” said British Prime Minister Theresa May, who was attending her first EU summit.
“It’s vital that we work together to continue to put pressure on Russia to stop its appalling atrocities, its sickening atrocities in Syria.”
French President François Hollande, who held talks with Russian leader Vladimir Putin and German Chancellor Angela Merkel on Wednesday, echoed the need to act.
“All the options are open as long as the truce is not respected and as long as there is a will to crush a city, Aleppo,” he said.
“I go into this European Council to convince the Europeans that we should apply all the pressure required to prolong the truce, to allow humanitarian aid to reach the population and to have a political discussion.”
But there were warning that the EU remains divided on how to deal with Russia; an agreement on imposing sanctions on Russia over the conflict in Ukraine took months to strike.
“One option is sanctions. I don’t think there’s unity but I think it should be on the table, that this should be an option for the future,” said Swedish Prime Minister Stefan Lofven.
A draft text circulated by diplomats says that Russia should allow “unhindered humanitarian access to Aleppo” and to other parts of Syria while calling “for an immediate cessation of hostilities and for resumption of a credible political process under UN auspices.”
The text also says “those responsible for breaches of international humanitarian law and human rights law must be held accountable.”