Shelling stopped abruptly at midnight on Saturday in the eastern Ukrainian city of Donetsk after President Petro Poroshenko ordered government forces to halt firing in line with a ceasefire agreement aimed at ending the country's bloody conflict.
Poroshenko, wearing the uniform of the armed forces supreme commander, said in a televised address in the capital Kiev that there was still "alarm" over the situation around Debaltseve, a key transport hub, where government forces have been hard pressed by encircling Russian-backed separatists.
The ceasefire, negotiated in four-power talks on Thursday, foresees creation of a neutral "buffer zone" and withdrawal of heavy weapons responsible for many of the 5,000 deaths in a conflict that has caused the worst crisis in Russia-West relations since the Cold War a generation ago.
Kiev and NATO have long charged that Moscow has supplied pro-Russian separatists in eastern Ukraine with arms and men, and Washington and its allies have slapped Russia with a series of economic sanctions. Russian President Vladimir Putin denies Moscow is involved in fighting for territory Putin calls "New Russia," although Western officials cite overwhelming evidence to the contrary.
Pososhenko warned on Saturday night that Ukraine, if it was slapped once, would not offer the other cheek. But, seated alongside armed forces chief of staff Viktor Muzhenko, he added: "I very much hope that the last chance to begin the long and difficult peaceful process for a political settlement will not be wasted."
"As a first step I now give the order to the armed forces of Ukraine ... to cease fire at 00:00 hours on February 15," he said.
Military spokesman Vladyslav Selezynov said the Ukrainian armed forces immediately fulfilled Poroshenko's order and the big guns fell silent in Donetsk and some other parts of the separatist-leaning east.
In the hours leading up to the ceasefire, heavy artillery and rocket fire roughly every five seconds had reverberated across Donetsk, the main regional city in the east which is under the control of the secessionists.
In Artemivsk, a town in government-controlled territory north of Debaltseve that has been hit twice in two days by rocket attacks, there was also silence at midnight.
U.S. Secretary of State John Kerry urged implementation of the ceasefire in a telephone call with his Russian counterpart Sergei Lavrov and expressed concern about efforts by Russia and the separatists to cut off Debaltseve, the U.S. State Department said.
U.S. President Barack Obama also expressed "deep concern" about the violence around Debaltseve in a telephone call with Poroshenko, the White House said.