Russian president Vladimir Putin has announced a ceasefire in Ukraine just hours after his Ukrainian counterpart Petro Poroshenko said Moscow had proposed "unacceptable" conditions at the Minsk peace talks.

The truce is set to start at midnight on Sunday 15 February.

The deal comes at the end of a marathon 12-hour period of talks between the leaders of France, Germany, Ukraine and Russia, which had appeared far from reaching a conclusive end to the hostilities that have killed more than 5,000 people.

Notably, the parties reportedly hadn't been able to reach an agreement on the demarcation line separating territories held by Russian-backed rebels from those under Kiev's control.

Separatist have gained ground in recent weeks, pushing government troops back from positions agreed in a September ceasefire deal.

Putin said that he and Poroshenko disagreed on assessing the situation in the key flashpoint of the government-controlled town of Debaltseve, a strategic transport hub between the Donetsk and Lugansk that has been the focus of intense fighting in recent weeks.

The Russian president said that the separatists had surrounded Kiev forces there and expected them to surrender, while Ukraine disagrees with that.

Separatist leaders Alexander Zakharchenko and Igor Plotnitsky had joined the contact group, which includes representatives from Ukraine, Russia and the Organization for Security and Co-operation in Europe (OSCE), but critics argued they were directly controlled by the Kremlin.

The Ukraine and the West have accused Putin of aiding the rebels with troops and weapons, but this has always been denied by the Kremlin.

In a break during the marathon peace summit, Poroshenko told AFP that negotiations were ongoing, but added: "Unfortunately, there's no good news yet. There are conditions that I consider unacceptable.

"There is always hope. We're in non-stop talks, as you can see, the situation is very difficult, Angela Merkel and President Francois Hollande are helping us a lot, but for now the situation is difficult."

Meanwhile, both rebels and government troops reported that fighting was continuing across the restive region.

The conflict has engulfed the region of Donetsk, with heavy shelling damaging key cities such as Donetsk and Kharkiv.

Earlier this week rebels killed at least seven civilians during rocket attacks in Kramatorsk, while Ukraine's volunteer Azov battalion launched an attack on separatists camped in Mariupol.