Ukraine's new president has enlisted support from the leaders of Germany and France for a call to his Russian counterpart Vladimir Putin as a ceasefire deadline looms.
President Petro Poroshenko is expected to be joined by German Chancellor Angela Merkel and French President Francois Hollande on the scheduled phone call on Sunday to the Russian leader on the eve of the deadline.
Sunday's teleconference is primarily meant to check on any visible shift in Moscow before the European Union and Washington consider unleashing biting sanctions against Russia's financial and defence sectors starting on Monday.
Both Ukraine and its Western allies have been seeking concrete steps from Russia to back the ceasefire between Kiev and pro-Russian militias in the hope of calming a deadly insurgency sparked by the country's new westward course.
On Sunday, Ukraine's military said there had been sporadic attacks by pro-Russian gunmen in the east, despite the ceasefire being in place.
The phone call also comes after pro-Kremlin rebels in Donetsk released four monitors from the Organisation for Security and Cooperation in Europe (OSCE) -- one woman and three men -- after being pressed by Putin to meet the terms of the tenuous truce with Kiev.
The OSCE observers looked tired but relieved as they were handed over by heavily-armed rebels to one of the group's representatives at a hotel in the eastern hub city of Donetsk.
"We are releasing the last four observers who were being held on the territory of the Lugansk People's Republic," the prime minister of the self-proclaimed Donetsk People's Republic told reporters.
"We consider that we have fulfilled all our obligations," Oleksandr Borodai said.
The first group of observers detained on May 26 in the Donetsk province were handed over to the OSCE on Thursday.
The Vienna-based organisation said the second team included nationals from Germany, the Netherlands, Spain and Russia.
The one-week truce had been due to expire on Friday at 7pm GMT, and will now expire at 7pm GMT on June 30, according to Ukraine's presidential website.