19 Ukrainian soldiers have been killed and 78 wounded in rebel attacks near the key railway town of Debaltseve, which government troops are defending, a military spokesman said on Wednesday.
"In shelling, rocket attacks and military clashes, Ukraine lost 19 soldiers including 17 members of the armed forces and two interior ministry soldiers," the spokesman, Vladyslav Seleznyov, told a briefing.
Rockets has killed more than 10 civilians and soldiers deep in Ukrainian government-held territory on Tuesday and rebels pushed on with an assault on an army-held rail junction, setbacks that showed Kiev's position worsening on the eve of peace talks.
Advances by pro-Russian rebels diminished hopes of a deal when Russia, Ukraine, France and Germany hold a summit in Belarus on Wednesday under a new Franco-German initiative to halt fighting in a war that has killed more than 5,000 people.
Representatives of the "Contact Group" meeting in Belarus on the Ukraine crisis denied a report by Russia's TASS news agency that a ceasefire deal had been reached in talks in Minsk. Rebel representative Denis Pushilin told Russian channel Rossiya24 it was too early to talk of any agreements and said the sides were taking a break.
TASS, quoting an unnamed source, earlier said the envoys from Russia, Ukraine, pro-Russian rebels and the OSCE security watchdog had agreed a ceasefire for east Ukraine, a monitoring mechanism and a scheme for withdrawal of heavy weapons.
However rebel representative Denis Pushilin told Russian channel Rossiya24 it was too early to talk of any agreements and said the sides were now taking a break.
He later told journalists he had handed over to the Ukrainian side a proposal of "political and military steps" towards de-escalation and that the talks would resume after the Ukrainian envoy considers them. He did not say whether the talks would continue on Tuesday or later on.
European officials say it is difficult to imagine the rebels agreeing to halt and go back to earlier positions after weeks during which they have been advancing relentlessly.
A Russian source quoted by the state RIA news agency said there were no plans to sign a document to resolve the conflict at the peace talks, and the main subject would be creation of a demilitarised zone.
The war and years of endemic corruption have nearly bankrupted Ukraine, where the currency collapsed last week. Ukraine is negotiating a rescue package with the International Monetary Fund and sources said that could be expanded dramatically to provide as much as $40 billion in aid.
The White House said U.S. President Barack Obama urged Russian President Vladimir Putin in a phone call on Tuesday to agree to a peace deal.
"If Russia continues its aggressive actions in Ukraine, including by sending troops, weapons, and financing to support the separatists, the costs for Russia will rise," the White House statement added.
The Kremlin, in its statement about the call, said Putin and Obama highlighted the need for the need for a political solution to the "internal" conflict in Ukraine.
The Kremlin also said the two leaders also noted the necessity to safeguard the rights of inhabitants of all Ukrainian regions, including Russian-speakers in the east.