The European Union signed an historic free-trade pact with Ukraine on Friday and warned it could impose more sanctions on Moscow unless pro-Russian rebels act to wind down the crisis in the east of the country by Monday.
Shortly after returning to Kiev from Brussels where he signed the pact, Poroshenko announced on his website that Ukraine had extended a ceasefire by government forces against pro-Russian separatist rebels by 72 hours until 10 p.m. on Monday.
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Ukrainian President Petro Poroshenko came to Brussels to sign a far-reaching trade and political cooperation agreement with the EU that has been at the heart of months of deadly violence and upheaval in his country, drawing an immediate threat of "grave consequences" from Russia.
Georgia and Moldova signed similar deals, holding out the prospect of deep economic integration and unfettered access to the EU's 500 million citizens, but alarming Moscow, which is concerned about losing influence over former Soviet republics.
The week-long ceasefire had been due to expire on Friday.
The extension was made, Poroshenko's website said, in line with a Monday deadline set by EU leaders for the rebels to agree to ceasefire verification arrangements, return border checkpoints to Kiev authorities and free hostages including detained monitors of the OSCE rights and security watchdog.
"We expect progress in the next hours," German Chancellor Angela Merkel said. "If we don't see any steps forward on any of the points, then we are also prepared to take drastic measures."
EU leaders said they were ready to meet again at any time to adopt significant sanctions on Russia. Diplomats said they could target new people and companies with asset freezes as early as next week. More than 60 names are already on the list.
Although it has drawn up a list of hard-hitting economic sanctions against Russia, the EU is still hesitating over deploying them because of fears among some member states of antagonizing their major energy supplier.
"We are talking about possible sanctions against Russia but we do not have to introduce sanctions for the sake of sanctions. We do have a need for a dialogue. I hope this dialogue will take place and we will have a real ceasefire," Poroshenko told a news conference in Brussels.
Poroshenko has drawn up a 15-point peace plan to defuse the crisis in eastern Ukraine, where hundreds of people have been killed in clashes between security forces and pro-Russian rebels.
Ukraine, Georgia and Moldova have made clear that their ultimate goal is EU entry, but Brussels, under pressure from voters weary of further expansion, has made no promise it will allow them in.
Poroshenko and national security chiefs said that during the next 72 hours recruitment centers for Russian fighters across the border in Russia should be closed.
Ukrainian government forces would have the right to end the ceasefire ahead of time in any areas where ceasefire conditions were not being implemented, Poroshenko's announcement said.