Ukraine's three-day ceasefire extension in pro-Russian eastern regions has been marred by isolated violence. Moscow's economy minister has warned that tougher Western economic sanctions will harm Russia.
Ukraine's government awaited signs from Russian President Vladimir Putin on Saturday that pro-Russian separatists would comply with European Union demands, including rebel withdrawals from border crossings and their acceptance of a truce-monitoring mechanism.
Progress is to be assessed during a telephone conference due late on Sunday between Ukraine's new President Petro Poroshenko and Putin, who on Friday backed the ceasefire's extension.
Poroshenko extended the tenuous truce when he returned to Kyiv from Friday's summit in Brussels, where he signed a landmark Ukrainian free trade and political association deal with the EU, despite Russian objections.
Isolated clashes, apparently without casualties, occurred in the eastern Ukrainian region of Donetsk on Saturday, according to the Interfax news agency and Ukraine's military.
Donetsk separatist leader Miroslav Rudenko claimed that government troops were using the extension -- which runs until 1900 UTC Monday -- to strengthen their positions.
Pro-government forces in turn accused rebels of shooting at soldiers at Kramatorsk airport.
In Washington, US State Department spokeswoman Marie Harf said the United States was ready to tighten financial and defense sector sanctions on Russia if the rebels failed to meet demands.
The EU summit on Friday also demanded that the rebels release all hostages, including international OSCE observers, and start substantial talks on a peace plan.
The 15-point plan was outlined by Poroshenko a week ago but the rebels refused to lay down their arms.
Russia facing economic impacts
A new round of Western "phase three" sanctions would impact Russia "seriously," Russia's Economy Minister Alexei Ulyukayev warned on Saturday, according to the Rossiya television channel.
He said the worst of three scenarios, whereby Western sanctions would apply to metals, fertilizers, oil and gas, would shove Russian economic growth rates "seriously into the negative."
So far, EU and US sanctions have targeted specific individuals and entities, with the EU reluctant to press ahead because it relies on Russia for part of its energy supplies.
The rating agency Moody's on Friday cut Russia's credit rating to "negative," citing a "geo-political event risk."
Twelve weeks of unrest in Ukraine have claimed more than 440 lives and displaced thousands of people, especially in eastern and southern regions.
The conflict deepened in February when Ukraine's previous president opted for closer ties with the Kremlin and ditched the very EU accord that Poroshenko signed on Friday.
ipj/tj (AFP, dpa, Reuters)