The leaders of France and Germany have backed Russia by calling for a new ceasefire in eastern Ukraine but told Vladimir Putin, the Russian president, to prevent separatist fighters and arms from crossing the border into Ukraine.
French President Francois Hollande and German Chancellor Angela Merkel told Putin on Thursday that it was important to reach a political solution quickly in the three-month-old conflict between government forces and separatists in the country's east.
In a three-way telephone conversation, they asked Putin to "exert all necessary pressure" on the separatists and to take "the concrete measures required to control the Russia-Ukraine border", Hollande's office said in a statement.
Russia denies accusations by Ukraine and Western governments that it has worsened the conflict by allowing fighters and weaponry to move freely into eastern Ukraine from Russia.
The Kremlin said in a statement that the three heads of state supported "a swift renewal of the ceasefire and a meeting of the contact group" on resolving the crisis.
The three leaders have had regular phone conversations on the conflict. They will also soon hold talks with Petro Poroshenko, the Ukrainian president, Hollande's office said.
Government forces have recently made gains against the separatists in the Russian-speaking eastern regions.
More than 200 government soldiers have been killed as well as hundreds of civilians and rebel fighters.
Also on Thursday, a spokesman for the Russian Foreign Ministry said Russia was willing to invite its Ukrainian counterparts to monitor the border together.
Alexander Lukashevich said Ukrainian border guards might be invited to patrol the border together at two border posts.
He said, however, that this would only be possible if a ceasefire was in place.
The rebels have several Ukrainian border posts under their control, and Ukraine has unsuccessfully demanded them back.
The pro-Russian rebels have been fighting government troops in eastern Ukraine for more than three months, leaving at least 400 dead.