The leaders of France and Germany spoke for more than two hours in a four-way phone call yesterday with Russia's Vladimir Putin and Ukraine's Petro Poroshenko, seeking progress before a Ukraine ceasefire expires.
Poroshenko's discussion with Putin, German Chancellor Angela Merkel and French President Francois Hollande was the latest in a series they have held in recent weeks in an effort to stop the fighting that has killed more than 400 people since April.
The four leaders will speak again by telephone today.
Ukraine extended its truce by 72 hours until tonight, coinciding with a deadline set by European Union leaders on Friday for pro-Russian rebels to agree ceasefire verification arrangements, return border checkpoints to Kiev authorities, free hostages and launch serious talks on implementing Poroshenko's peace plan.
The separatist rebels in eastern Ukraine on Saturday released a second group of four monitors from the Organisation for Security and Cooperation in Europe (OSCE) who had been seized on May 29.
But the ceasefire appeared under threat when three members of the Ukrainian military were killed in a rebel attack near the eastern city of Slaviansk.
The four observers were released and met by an OSCE official in the eastern city of Donetsk. "They're in good health, they're in good spirits," OSCE spokesman Michael Bociurkiw said.
OSCE lost contact with four monitors from its Donetsk team and four monitors from its Luhansk team in late May. The members of the Donetsk team were freed earlier last week.
"We have fulfilled our obligations before the Ukrainian side. All eight observers have been released," Alexander Borodai, one of the leaders of the insurgents, said after the release
Additional reporting by Reuters