Under terms of a peace agreement signed in Minsk in February, local elections were meant to be held in the separatist regions along with the rest of the former Soviet republic this autumn. But Kiev has since said they cannot take place in the east because of continued security problems there.
The separatists, in response, scheduled their own ballot for October and November, angering Kiev which said it would not recognize the results.
"Putin promised to make every effort and to let us know no later than Tuesday that this decision [to cancel elections] will be taken," Poroshenko said in a televised interview.
The comments follow talks on Friday between the leaders of Russia, Ukraine, France and Germany, who met to discuss the Ukraine peace process.
At the meeting French President Francois Hollande said it would take time to organize elections in eastern territories that respect international standards and as a result, the so-called Minsk peace process would run beyond its deadline, into next year.