A cease-fire that went into effect Sunday in eastern Ukraine appeared largely to be holding, officials said, except for around the strategic railway hub of Debaltseve.

Heavy fog shrouding sodden fields muffled the sound of artillery, but regular shelling could still be heard Sunday from Luhanske, a town about 9 miles to the northwest. Associated Press journalists were blocked from moving closer by Ukrainian troops, who said it was not safe to travel ahead.

The cease-fire has kindled slender hopes of reprieve from the conflict between the government troops and Russian-backed separatists that has claimed more than 5,300 lives since it began in April.

Attention will be focused in the coming days on Debaltseve, where Ukrainian forces have for weeks been fending off severe onslaughts from the rebels. The town is a railway link between the main separatist-held cities of Donetsk and Luhansk.

This latest cessation of hostilities was agreed after a marathon session of diplomacy last week that brought together the leaders of Ukraine, Russia, Germany and France for talks in the capital of Belarus, Minsk.

Under the deal hammered out at those negotiations, the progress of the cease-fire is to be monitored by observers from the Organization for Security and Cooperation in Europe. Ukrainian Foreign Minister Pavlo Klimkin complained Sunday that rebels had barred OSCE monitors from reaching Debaltseve to report on developments there.

"It quite clearly shows who is in breach of the Minsk agreement," Klimkin said.

The press office for government military operations in the east said in a statement that Sunday was characterized by a relative degree of calm.

"There has unfortunately not been a total cessation of fire, however," the statement said.

A spokesman for the Ukrainian army general staff, Vladislav Seleznyov, said during a morning briefing that shelling was noted 10 times, with all but one incident occurring in the Debaltseve area. Another military spokesman, Andriy Lysenko, said Sunday that nine Ukrainian troops had died over the previous day's unrest.

The rebels have in turn accused the Ukrainians of deploying artillery in the Debaltseve area shortly after midnight. Also, they argue that since they have fully encircled Debaltseve, the territory should be deemed as being theirs.

But Ukrainian President Petro Poroshenko, as he issued the cease-fire order at one minute after midnight Kiev time Sunday (5:01 p.m. EST), said the road to the town remained open and that Ukrainian troops there had been resupplied with ammunition.

At an army checkpoint along the road to Debaltseve, a commander said the shelling appeared to have come from an area beyond Debaltseve controlled by "gangs other than the Russians and the separatists, such as Cossacks." The commander, who would identify himself only as Sanich, said these forces "submitted to no authority."

Donetsk, the separatist stronghold, was quiet Sunday morning with no shelling from government forces, the Donetsk News Agency, a separatist mouthpiece, reported, citing the city administration.

In the Luhansk region, two civilians were killed shortly after midnight in the town of Popasne as a result of shelling, regional authorities said. The town lies directly on the front line, only a few kilometers (a mile or two) from the nearest separatist positions.

The shells hit a shop, a medical clinic and a private residence, Luhansk Governor Hennadiy Moskal said in a statement. "The owners of the house — an 87-year-old man and a 67-year-old woman — died under the ruins," Moskal said.

The hours before the cease-fire were marked by ferocious battles around Debaltseve, as Ukrainian armed forces undertook desperate attempts to gain control over a highway linking the town to their rearguard.

The U.S. State Department said satellite images from eastern Ukraine offer "credible pieces of evidence" that the Russian military has deployed larger amounts of artillery and multiple rocket launchers around Debaltseve to shell Ukrainian forces. The images could not immediately be verified.

Russia has repeatedly denied Western claims that it has sent troops and equipment to aid the rebels.

Cessation of hostilities is only the first in a series of planned steps agreed to in Minsk.

Withdrawals of heavy weaponry from the front line, creating a zone roughly 30-85 miles wide, depending on the caliber of the weapons, are to begin Monday and be completed in two weeks. No provisions are envisioned for the withdrawal of troops.

The peace plan also requires the Ukrainian government to resume paying pensions and state benefits to citizens in rebel-held territory. Ukraine's financial blockade against the rebels has led to a catastrophic collapse in living standards in eastern Ukraine, depriving the poorest of any immediate means of support.