The leaders of Russia, Ukraine, France and Germany have reached a ceasefire deal after 17 hours of talks in Minsk, Belarus, on the Ukrainian conflict.

The ceasefire will come into force on Sunday as part of a deal that also involves the withdrawal of heavy weapons from the front line.

Russian president Vladimir Putin was the first to announce the deal, saying: “We have agreed on a ceasefire from midnight 15 February.”

Putin added: “There is also the political settlement. The first thing is constitutional reform that should take into consideration the legitimate rights of people who live in Donbass. There are also border issues. Finally there are a whole range of economic and humanitarian issues.”

The German chancellor, Angela Merkel, who helped to broker the deal alongside the French president, François Hollande, said “we now have a glimmer of hope”, but added that the leaders were under no illusions and that “there is very, very much work still to do”.

Merkel also confirmed that Putin put pressure on the separatists to agree a truce.

Hollande said the deal covered all the contentious issues, including border control, decentralisation, and the resumption of economic relations, but also warned that much more needed to be done to resolve the crisis.

Hollande and Merkel will ask the European Union to support the agreement later on Thursday.

European Union foreign policy chief Federica Mogherini sounded a note of caution, saying the Minsk agreement was important but not definitive. She added that she did not expect EU leaders to discuss sanctions against Russia at their summit on Thursday after the deal. 

Ukraine’s president, Petro Poroshenko, said: “The main thing which has been achieved is that from Saturday into Sunday there should be declared without any conditions at all a general ceasefire.”

Speaking after the talks, Donetsk rebel leader Alexander Zakharchenko called the treaty a “major victory for the Luhansk and Donetsk people’s republics”. Luhansk leader Igor Plotnitsky said they would “give Ukraine a chance, so that the country changes its constitution and its attitude”.

But despite the celebratory words, the fledgling peace process remained very fragile. Zakharchenko warned that all “responsibility will be on Petro Poroshenko”, and that the peace process would fall through if Kiev violated the new agreements, Russian news agency Interfax reported.

“All the points require additional approval, and for this reason there will be no meetings and new agreements if any violations take place,” Zakharchenko said.

Residents of Donetsk, where civilians have continued to be killed by shelling this week, greeted the news of the peace agreement with cautious optimism. A small group of people rallied outside the rebel government’s headquarters in the Donetsk regional administration building, and a woman on stage declared that “today is a holiday.”

More hardcore supporters of the rebels were disappointed with the new agreement. The popular Russian nationalist publication Sputnik i Pogrom called the Minsk treaty a “betrayal of all that the rebels fought for, including some of our readers” and derided the “clownish half-autonomous status” offered to the breakaway republics.

Earlier, Ukraine had played down speculation about a possible ceasefire agreement, accusing Russia of imposing “unacceptable” conditions.

At one point during the negotiations Putin signalled his apparent frustration at the lack of progress by snapping a pen or a pencil.

More than 5,300 people have died since April in the conflict between Ukrainian forces and Russia-backed separatists in two eastern provinces, and the bloodshed rose sharply in recent weeks.

Although the Minsk agreement represents a breakthrough in a long-frustrated peace process, several key points will be difficult and time-consuming to achieve.

It remained unclear what actions were to be taken in Debaltseve, the current major point of contention between the warring sides in eastern Ukraine. Pro-Russian fighters have been trying to take the town and its railroad junction from Ukrainian forces in weeks of heavy fighting, with violence escalating in the buildup to the peace talks.

The rebels have said they have Debaltseve surrounded, while the Ukrainian military has repeatedly denied this. But a volunteer battalion commander said on Thursday morning that Kiev’s forces were storming Lohvynove, a town located along the only highway leading out of Debaltseve to Ukrainian positions, suggesting that the troops really were surrounded.

Speaking to Russian channel RT, Putin said he had ordered “military experts” to look into how to solve the situation in Debaltseve peacefully. The Minsk agreement stipulates that the rebel republics withdraw their forces from the demarcation line laid down in the September ceasefire, and that Kiev withdraws its forces from the current de facto frontline.

“If it really is surrounded, then according to the normal logic of things, those who are surrounded will make attempts to break out, and those who are outside will make attempts to organise a corridor for the surrounded troops to leave,” Putin said.

“Look what the Russians are now bargaining for,” tweeted Ukrainian foreign ministry representative Dmytro Kuleba on Thursday, with a link to rebel claims that they had Debaltseve surrounded. “Without Debaltseve, the [Luhansk and Donetsk people’s republics] are in a transportation bind.”

Another particularly difficult point to implement will be re-establishing Kiev’s control of the border, through which Russian volunteers, arms and allegedly troops have been coming to the rebels’ aid. Many of the border crossings with Russia are under rebel control, and the boundary between the two countries is notoriously porous anyway. Poroshenko said Kiev will only restore full control of the border by the end of 2015.

The US president, Barack Obama, has faced rising calls at home to send military aid to Ukraine, but European leaders fear it would only aggravate the violence. Russia, meanwhile, faces a severe economic downturn driven in part by sanctions the west has imposed for supporting the separatists with troops and equipment, which Moscow vehemently denies it is doing.

The urgency felt by all sides appeared to be underlined by the extraordinary length and discomfort of the talks between the leaders of Ukraine, Russia, France and Germany. They sat down with each other Wednesday evening in the Belarusian capital and the talks continued as sunrise neared on Thursday.

In a diplomatic blitz that began last week, Merkel and Hollande visited Kiev and Moscow to speak to Poroshenko and Putin, paving the way for the marathon session in Minsk.