Peace talks in Minsk aimed at ending the fighting in eastern Ukraine ended without progress on January 31.
Ukraine's representative at the talks, former President Leonid Kuchma, told Interfax that the two separatist representatives at the talks issued ultimatums and refused to discuss a plan "for a quick cease-fire and a pullback of heavy weapons."
The more than four hours of talks, held at the Belarusian Foreign Ministry building, included Russian Ambassador to Ukraine Mikhail Zurabov, Organization for Security and Cooperation in Europe representative Heidi Tagliavini, and rebel representatives Denis Pushilin and Vladislav Deinego.
Pushilin, for his part, said the separatists will reject ultimatums and accused Ukraine of blocking the peace process.
Kuchma also criticized the two main, self-proclaimed separatist leaders in eastern Ukraine -- Aleksandr Zakharchenko and Igor Plotnitsky -- for not attending the talks as signatories of the original Minsk agreements signed in September.
Pushilin told journalists in Minsk before the talks began that Zakharchenko and Plotnitsky are "fully occupied" dealing with the consequences of the Ukrainian bombardments.
Pushilin repeated after the talks that the two main separatist leaders will attend peace talks only after Ukrainian President Petro Poroshenko declares an immediate cease-fire and pulls back heavy weaponry and their presence is needed to sign "the final document."
Pushilin added that Kuchma was not currently authorized to sign a final document on behalf of Ukraine.
OSCE officials said before the talks that they hoped for a "binding" truce that would allow an "unrestricted supply of basic goods" as well as humanitarian aid to go to the civilians who are most affected by the fighting.
The Kremlin said Russian President Vladimir Putin, German Chancellor Angela Merkel, and French President Francois Hollande spoke via phone on January 31 before the talks to discuss the increased violence in eastern Ukraine and expressing hope that a new cease-fire will be the main point of the Minsk peace talks.
The peace talks in the Belarusian capital were being looked on as a chance to reduce the increased hostilities between separatist fighters and Ukrainian troops that killed 15 and wounded more than 30 Ukrainian soldiers on January 30-31, the most casualties Ukrainian forces have suffered since the often-violated cease-fire was signed in Minsk on September 5.
A total of more than 5,100 people have been killed and hundreds of thousands have hed to flee their homes since the fighting began in April.
Ukrainian officials want separatist forces to pull back to the line of contact as outlined in the Minsk agreement, but the rebels are balking at that request as they have gained more than 500 square kilometers of Ukrainian territory since September and sit just outside the important seaport of Mariupol.
Fighting has been particularly intense in recent days in and around the city of Debaltseve, an important transportation hub some 50 kilometers northeast of the city of Donetsk.
Rebel representatives say they have nearly encircled thousands of Ukrainian forces in and near Debaltseve, which is caught in the artillery crossfire of the two sides.
The fight for the city -- which has been without power, water, and gas for some 10 days -- has led hundreds of people to flee the area.
Scores of others have been injured and taken to a nearby hospital that is controlled by Ukrainian forces.
Ukrainian Prime Minister Arseniy Yatsenyuk said on January 31 that some 1,000 residents have been evacuated from Debaltseve in recent days.
Vyacheslav Abroskin, head of police for the Donetsk region, said 12 people had been killed by shelling in Debaltseve, which had some 25,000 residents before the fighting began.
Rebel leaders had said before the talks that if they failed their offensive would continue.
"Should the negotiations collapse...the Donetsk and Luhansk People's Republics reserve the right to pursue their offensive until the entire Donetsk and Luhansk regions are freed" of Ukrainian troops, Pushilin and Deinego said in a joint statement.
They also demanded that the new border outlining rebel-held territory should run along the current front.
The latest violence has alarmed Ukraine's Western allies, with U.S. Secretary of State John Kerry announcing plans to visit Kyiv on February 5 for talks with Poroshenko and Yatsenyuk.
The State Department said Kerry will then meet his Russian Foreign Minister Sergei Lavrov on the sidelines of the Munich security conference.
Western governments and Ukraine accuse Russia of arming and training the rebels, who are deploying sophisticated and heavy weaponry, including dozens of tanks and multiple-rocket launchers.
Russia denies aiding the rebels.
The 28-nation EU on January 29 extended through September a first wave of targeted sanctions it had imposed on Moscow and Crimean leaders in the wake of Russia's March seizure of the Black Sea peninsula from Ukraine.
EU foreign ministers also agreed to start work on further "appropriate action" if Moscow and the rebels continued breaching the original terms of the collapsed September truce.