The leaders ofFrance,Germany and Ukraine said on Monday that observers from the Organization for Security and Cooperation in Europe must have "free access" for their work in eastern Ukraine.

French President Francois Hollande's office said Hollande, German Chancellor Angela Merkel and Ukrainian President Petro Poroshenko spoke on Monday to take stock of the situation since Sunday's ceasefire.

"They expressed their worry over the continued fighting in Debaltseve. They also noted their desire that the OSCE observers have free access to pursue their work on the ground in an objective manner," Hollande's office said.

The OSCE said on Sunday that rebels in eastern Ukraine refused to allow its monitors to reach the encircled town of Debaltseve after the ceasefire took effect. The rebels have said the ceasefire does not apply to Debaltseve, scene of the worst fighting in recent weeks.