Kyiv and pro-Russian rebels traded accusations over deadly attacks in eastern Ukraine as planned peace talks in Minsk were reportedly postponed.
Denis Pushilin, who represents rebels holding territory in Ukraine's Donetsk region, said he and Luhansk separatist representative Vladislav Deinego would leave Minsk for Moscow.
Meanwhile, former Ukrainian President Leonid Kuchma, who represents Ukraine at the talks, said he was ready to fly to Minsk on January 31.
"We expect the signing of a document on further developing the Minsk agreements of September 15 and of the peace plans of Presidents [Petro] Poroshenko [of Ukraine] and [Vladimir] Putin [of Russia]," Kuchma told the Interfax Ukraine news agency.
But Kuchma insisted that the leaders of the self-proclaimed Donetsk and Luhansk people's republics, Aleksandr Zakharchenko and Igor Plotnytsky, participate in negotiations in order for some decisions to be made.
The Belarusian Foreign Ministry had said on January 29 that talks involving representatives of Ukraine, Russia, the separatists holding territory in eastern Ukraine, and the Organization for Security and Cooperation in Europe would meet in Minsk for talks aimed at ending hostilities.
Pushilin said the Russian-backed separatists would agree to a cease-fire with Ukrainian forces based on the current line of contact between the two sides.
Rebels have taken hundreds of square kilometers from Ukrainian forces since the first line of contact was established in a cease-fire agreement in September.
But Pushilin added that separatists are prepared to take more territory in the Donetsk and Luhansk regions if Ukrainian forces launch an "offensive."
PHOTO GALLERY: Death In Donetsk
Meanwhile, the city administration in Donetsk, one of two separatist-held provincial capitals, said six people were killed when shells hit a cultural center on January 30 and that two others were killed when a shell hit a trolleybus.
The Ukrainian military said that five of its soldiers were killed and 23 wounded in the previous 24 hours.
It said rebels used mortars, rockets, and artillery in attacks on government positions at Debaltseve, a key junction between Donetsk and Luhansk, and in the vicinity of the strategic Azov Sea coastal city of Mariupol.
Fighting has escalated this month in the conflict, which has killed more than 5,100 people since April.
The rebels have made gains recently in what the United States has called a "Russian-backed offensive" that violates the terms of an agreement on a cease-fire and steps toward peace signed in Minsk in September.
A senior rebel leader, Aleksandr Zakharchenko, said on January 23 that the rebels would push to the borders of the Donetsk province, casting deep doubt on their commitment to any cease-fire.
Zakharchenko said on January 30 that rebel forces had surrounded government units near Debaltseve and that the soldiers' lives would be spared if they surrendered their weapons.
WATCH: Where the shelling never stops
The Ukrainian military said its forces were holding their positions and returning artillery and mortar fire when fired upon.
There was no immediate comment from Kyiv on Zakharchenko's claim that Debaltseve was surrounded.
The government-held town is a key rail and road junction in the east.
Rebels accuse the military of targeting civilian areas, while the government and rights groups say the separatists put civilians at risk by firing from civilian areas.
Footage from Donetsk showed four covered bodies near the cultural center, in addition to the body of a dead man in a car, and what looked like an elderly man in a pool of blood near a damaged trolleybus.
The separatists blamed government forces. Kyiv said the shelling was carried out by the rebels to ruin the chance of peace talks. Both sides have made similar allegations throughout the conflict, which are impossible to verify.
In Debaltseve, regional police chief Vyacheslav Abroskin said in a Facebook post that seven civilians were killed on January 30 by separatist shelling of their homes. Earlier he reported another seven civilians killed in and around the town in the previous 24 hours.
Rocket attacks from rebel-held territory that killed at least 30 civilians in Mariupol on January 24 have prompted Western governments to step up criticism of the separatists rebels and Russia, which Kyiv and NATO says has supported the rebels with troops and weapons during the conflict.
The European Union decided on January 29 to extend until September an initial group of sanctions against Russian and pro-Russia separatist officials due to the continued fighting in eastern Ukraine and has plans for further action.
EU foreign ministers decided to extend sanctions imposed after Russia's annexation of Crimea last year until September, instead of letting them expire in March. They also agreed to draft a list of additional individuals to be potentially hit with sanctions early next month.
Russia said the decision would further damage relations, and suggested it could hurt diplomatic efforts to end the conflict.
A Russian Foreign Ministry statement blamed Kyiv for the escalation in fighting.
Ukrainian President Petro Poroshenko said on January 29 that any peace talks should lead to "an immediate cease-fire and the withdrawal of heavy weapons from the line of contact" in eastern Ukraine.