A cease-fire brokered by Angela Merkel and François Hollande went into effect in Ukraine last night, the New York Times reports. Aleksandr Zakharchenko, leader of the breakaway Donetsk People's Republic, has announced that it would not apply to Debaltseve, one of the war in Ukraine's key battlefields.

Debaltseve, which the Times describes as "a critical railway hub," has been the scene of intense fighting in recent weeks as Ukrainian troops under siege there defended the city from rebel troops who strove to capture it before the cease-fire was passed. From the Times:

Just after the midnight deadline, Ukraine's president, Petro O. Poroshenko, went on national television saying he had ordered Ukraine's armed forces to halt their fire in the contested eastern portion of the country. In his earlier statement, Mr. Zakharchenko, the head of the self-declared Donetsk People's Republic, also said he had ordered his forces to halt combat all along the front line in eastern Ukraine, as required in the Minsk agreement, but not near Debaltseve. He also indicated that rebel forces would not allow the approximately 8,000 Ukrainian troops who are there to leave.

"We will block all attempts to break out," he said. "I have given the order."

Poroshenko said that if the cease-fire—which appears to be holding elsewhere—deteriorates he will ask the Ukrainian parliament to declare martial law, the Times reports.

While rebel forces have Debaltseve surrounded, neither they nor the Ukrainian military fully control the road connecting the city with government forces in Artemivsk, the Guardian reports. Vladimir Putin has suggested that Ukrainian forces should abandon the city, a proposition which the Kiev government has refused.

Shelling resumed outside city, after a few hours of quiet, around 6 o'clock Sunday morning. "There's no ceasefire here," a Ukrainian soldier told the Guardian's Alec Luhn. "It's a present from Putin," said another soldier, referring to the mortar fire.

[Photo credit: AP Images]