Kiev and breakaway republics say ceasefire mostly being observed, but mortar fire is heard east of Luhanske on highway to Debaltseve

The fighting in east Ukraine dropped in intensity on Sunday, but the first day of a ceasefire deal still saw fighting, especially around the contested town of Debaltseve.

The deal to end the conflict, which has killed more than 5,000 people since it flared up last spring, was agreed after marathon talks last Wednesday in Minsk, Belarus, attended by the Ukrainian and Russian presidents as well as François Hollande and Angela Merkel.

After negotiations that went on throughout the night, a deal was agreed that called for a ceasefire to begin at midnight on Sunday, with the broad outline of a further political settlement also sketched. There remains widespread scepticism on all sides that the ceasefire can hold, not least because it is similar to a September deal that broke down almost immediately.

The four leaders spoke by telephone on Sunday and discussed the “difficult situation around the town of Debaltseve”, according to a Kremlin statement. Earlier in the day, John Kerry, the US secretary of State, spoke by telephone with his Russian counterpart Sergei Lavrov and urged the Russians to back the “full implementation” of the ceasefire.

Facebook Twitter Pinterest Residents in Svitlodarsk, eastern Ukraine. Photograph: Gleb Garanich/Reuters

Kiev and the breakaway republics in the east said fighting had quieted and the ceasefire was mostly being observed on Sunday afternoon. But the Guardian heard mortar fire to the east of Luhanske on the highway to Debaltseve, where up to 8,000 Ukrainian troops have been under rebel attack for weeks.

Soldiers at the last checkpoint in Luhanske said the guns had gone quiet after the midnight ceasefire, but shelling of Ukrainian positions in the area had resumed at around 6am – a report confirmed by the press service of Kiev’s “anti-terrorist operation”.

South of Luhanske is a 10-mile stretch of deadly road that is often shelled by rebels and reportedly mined, largely cutting off Debaltseve from the rest of the Ukrainian forces. Farther north on the highway, a destroyed troop transport truck was still smoking.

“There’s no ceasefire here,” said a soldier who would give only his first name, Andrei. “It’s a present from Putin,” joked another soldier, gesturing in the direction of the shelling.

The soldiers said Ukrainian forces were not shooting back, but some of the shelling to the east of Luhanske sounded like outgoing fire. Ukrainian army command said its forces were observing the ceasefire but would return fire if attacked or if the rebels shelled residential areas. The breakaway Donetsk People’s Republic said Ukrainian forces had shelled two rebel-controlled areas with machine guns and multiple rocket launchers shortly after 1am.

After the peace plan negotiations in Minsk, Vladimir Putin suggested that Ukrainian forces were surrounded and should give up the town, but Kiev has rejected this idea. Andrei showed the Guardian a text message telling Ukrainian troops they had been betrayed and would not be killed if they surrendered to rebels, which he said had been sent en masse to phones in the area near Debaltseve.

Ukrainian ambassador-at-large Dmytro Kuleba said the ceasefire had been occasionally violated during the night, but Kiev was ready to withdraw heavy weapons if the rebels did the same.

Facebook Twitter Pinterest Members of the Ukrainian armed forces near Debaltseve, eastern Ukraine. Photograph: Gleb Garanich/Reuters

“Debaltseve is, and will remain, one of the hottest spots,” Kuleba said. “In general, the truce is being observed here, but we expect that it will be the critical place in terms of facilitating a real ceasefire.”

The philosophy that the opposing sides could answer if attacked, a formula that led to the complete disintegration of the fraught ceasefire declared in September, is still in effect.

The rebels have said the ceasefire does not apply to Debaltseve and that Ukrainian forces will be attacked if they attempt movements other than to surrender. Putin’s spokesman, Dmitry Peskov, said the ceasefire agreements should be implemented in full, but did not specify whether the Kremlin believed Debaltseve to be exempt from the agreement.

Putin is believed to have pushed in Minsk for the ceasefire to come into effect much later, possibly with the hope that the rebel forces could take the town before the ceasefire began. Russia has insisted that it is not party to the conflict and rubbished evidence that it has backed the separatists with cash, weapons and, at times, regular troops.

The Minsk deal stipulates that both sides must withdraw weapons from the front line to create a buffer zone between 50 and 140 km (31 to 87 miles) wide, depending on the range of the weapons. Much of the conflict has involved both sides using extremely inaccurate weapons to shell each other, resulting in frequent civilian casualties.

According to the deal, Ukraine should also retake control of the border with Russia, which is currently fully under the control of the rebel forces and is used as a supply route from Russia for weapons and fighters. However, the agreements stipulate that border control will only come after local elections are held in the region and autonomy granted to the regions, though it is difficult to see how this process will work. Indeed, it appears more likely that if the ceasefire does hold, Kiev will essentially have to pay to support the rebel-held territory but will not have any political control.

The opposing sides appeared to be using the ceasefire to strengthen their positions. Three trucks full of Ukrainian soldiers in full battle gear were waiting on the highway leading to Luhanske, and a squad commander from a nearby volunteer battalion admitted Ukrainian forces were reinforcing their positions toward Debaltseve.

Ukrainian soldiers said their positions in the village of Zolote in the Luhansk region had been shelled in the early hours of the morning. According to Luhansk governor Gennady Moskal, fighting had quietened in his region, but a “complete ceasefire has not happened” and active fighting was ongoing in a few areas. The government-controlled town of Popasna was attacked with Grad rockets, killing an elderly couple whose their house collapsed on them, he said.

The Azov volunteer battalion said fighting had continued on a second major front near the coastal city of Mariupol, where 50 men from the battalion were injured and three killed on Saturday fighting for the town of Shirokine between government-controlled Mariupol and rebel forces near the Russian border.