Ukraine's government has massed military vehicles near the rebel-held eastern cities of Donetsk and Luhansk. The Kremlin says the leaders of Russia, Germany and France have talked by phone and called for a new ceasefire.
Tanks and military vehicles were seen massed 20 kilometers (12 miles) from Ukraine's eastern hub of Donetsk on Thursday, according to the French news agency AFP.
The Kremlin said Russian President Vladimir Putin, German Chancellor Angela Merkel and French President Francois Hollande had held a telephone conference on Thursday and agreed again on the need for a ceasefire and talks as soon as possible.
Hollande's office said the trio would soon have a four-way telephone conference with Ukrainian President Petro Poroshenko.
Kyiv, which has largely ignored Western calls for a negotiated truce with rebels after seizing their previous strongholds of Slovyansk and Kramatorsk, said early on Thursday that three Ukrainian soldiers had been killed in the past 24 hours.
It said two had died when their armored vehicle hit a landmine planted by separatists.
The leader of self-proclaimed "Luhansk People's Republic," Valery Bolotov, claimed that a number of Ukrainian troops had been killed in fighting around Luhansk airport, which is controlled by government forces.
Conflict zone 'halved'
President Poroshenko said separatist withdrawals had halved the size of the conflict zone. He said late Wednesday there would be no talks until the rebels disarmed and released prisoners.
Separatist leaders warned that any attempts to attack Donetsk, a city of one million, would result in high bloodshed.
An advisor to Ukraine's interior ministry, Stanislav Rechinsky, said there would be "no air or artillery strikes," against either Donetsk or Luhansk, but indicated that military operations could last a further month.
Ukraine's three-month-long conflict has already claimed more than 500 lives.
Further EU sanctions
On Thursday, the European Union imposed economic sanctions on a further 11 persons, mainly against pro-Russian separatists.
That raises the total number under sanction, including Russians, to 71, facing travel bans and asset freezes following the annexation of Crimea in March.
A Donetsk rebel leader Andrei Purgin said the sanctions would not affect his "work."
"We are not planning to travel to Europe and none of us has accounts in European banks," Purgin said.
iIpj/crh (AFP, dpa, Reuters) Kyiv forces retake Ukraine rebel stronghold