President Petro Poroshenko said he ordered government forces to stop hostilities at 2030 IST following a protocol signed by representatives of Ukraine, Russia, the rebels and the Organisation for Security and Cooperation in Europe.
"I count on this agreement, including the ceasing of fire and the freeing of hostages, to be precisely observed," Poroshenko said in a statement.
Heidi Tagliavini of the OSCE told reporters the deal reached at talks in the Belarusian capital of Minsk consisted of 12 points but she did not immediately spell them out before heading back into the talks.
But Igor Plotnitsky, the insurgent leader for the Luhansk region, told reporters "this doesn't mean that our course for secession is over" a statement that reflected deep divisions which threaten to derail peace efforts.
More From This Section
Since mid-April, Moscow-backed separatists have been fighting government troops in eastern Ukraine in a conflict the UN estimates has killed nearly 2,600 people.
A NATO military officer told The Associated Press yesterday that the ranks of Russian soldiers directly involved in the conflict have grown.
The shelling appeared to indicate that rebels had partially surrounded the area and were probing its defenses.
The seizure of Mariupol would give the rebels a strong foothold on the Sea of Azov and raise the threat that they carve out a land corridor between Russia and Crimea. If that happens, Ukraine would lose another huge chunk of its coast and access to the rich hydrocarbon resources the Sea of Azov is believed to hold.