Ukrainian President Petro Poroshenko and the main pro-Russian rebel leader said they would both order cease-fires on Friday, provided that an agreement is signed on a new peace plan to end the five-month war in Ukraine's east.

The breakthrough came after a week in which the pro-Moscow separatists scored major victories with what NATO says is the open support of thousands of Russian troops.

Speaking on the sidelines of a NATO summit in Wales, Poroshenko said the cease-fire would be conditional on a planned meeting going ahead in Minsk on Friday of envoys from Ukraine, Russia and Europe's OSCE security watchdog.