Peace talks between pro-Russian rebels and the Ukrainian government scheduled for Friday (30 January) were cancelled amid lethal fighting in eastern Ukraine.
In recent weeks the region has witnessed some of the deadliest violence since the conflict erupted in April last year.
A battle raged around the strategic town of Debaltseve on Friday, with some sources reporting that rebels had captured the town of Vuhlehirsk.
Russian state media reported that 12 civilians were killed in Donetsk, although the reports have not been verified.
More than 5,000 people have been killed in the fighting, according to UN figures. Representatives from Ukraine, Russia and the rebel fighters were due to meet on Friday, although the talks have now been shelved.
Pro-Russian separatist rebels had said they were travelling to the Belarusian capital of Minsk for talks over the conflict in eastern Ukraine.
However, they soon announced that no meeting was to take place and that they were flying back to Moscow, Reuters reported.
The rebels had previously warned that they would not seek to negotiate with Kiev as they had won a series of military victories on the ground.
The pro-Russian separatists recently took control of Donetsk airport and launched an attack on the port city of Mariupol, leading to the deaths of dozens of civilians.