Ukraine crisis: Fighting rages on despite declared truce
Pro-Russian separatists have carried out several attacks on Ukrainian troops despite a unilateral ceasefire declared by Kiev, Ukrainian officials say.
They say at least six border guards had been injured in shelling in the east.
The rebels earlier dismissed the week-long truce called by President Petro Poroshenko, the first step of his peace plan announced on Friday.
On Saturday, however, Russian President Vladimir Putin said he backed the plan - if it included talks with the rebels.
Mr Putin also said Ukraine must make compromises with the rebels.
He repeated the Kremlin's earlier criticism of the plan, saying that the temporary ceasefire which accompanied the proposals must not be offered as an ultimatum.
Meanwhile, the US imposed sanctions - including asset freezes - against seven pro-Russian leaders in Ukraine.
Western leaders have threatened additional sanctions against Russia, which they accuse of stoking tension in Ukraine. Moscow denies the claim.
In a separate development, Mr Putin ordered forces in Russia's central military district to be put on full combat alert for a week.
The drill does not affect troops near the border with Ukraine. Mr Putin has ordered several such alerts to test combat readiness in recent months.
Overnight, the separatists attacked three Ukrainian border posts in the Donetsk and Luhansk regions, Kiev said.
The rebels shelled the posts with rocket and mortar fire, injuring six border guards.
The gunmen also attacked Ukrainian forces outside the Kramatorsk airfield, in the Donetsk region.
The Ukrainian forces returned fire, and all the attacks were repelled, Kiev said. However, Ukraine's border guard service said its personnel at the Izvaryne post, Luhansk region, were forced to retreat into Russian territory.
A number of casualties were reported among the separatists.
Mr Poroshenko on Friday declared the ceasefire to give rebels time to disarm. It became effective from 22:00 local time (19:00 GMT).
The president also unveiled proposals for the peace plan involving decentralising power, holding early elections, and creating a 10km (six-mile) buffer zone on the Ukrainian-Russian border.
Rebel leaders have said they will not disarm until government troops have left the east.
Pavel Gubarev, self-styled governor of the "Donetsk People's Republic", said there was no ceasefire near Slovyansk, a bastion of separatist forces.
"There is shooting all the time, and this ceasefire that Poroshenko is talking about is just fake. The Ukrainian forces are either not under his control, or he is just a liar.''
The US and European Union leaders have previously imposed sanctions after Russia annexed the Ukrainian region of Crimea in March.
On Friday, the US Treasury Department said it had blacklisted seven rebel leaders, including self-proclaimed mayors, governors and commanders in chief of cities under siege by Ukrainian forces.
Their assets in the US will be frozen and US firms will be banned from dealing with them.
US officials also said "scalpel" sanctions against Russia's defence, finance and high-tech industries were being considered.
US President Barack Obama had spoken separately to French President Francois Hollande and German Chancellor Angela Merkel, a White House statement said.
The leaders had agreed the US and EU would "co-ordinate additional steps to impose costs on Russia" if Moscow did not try to "de-escalate the situation in eastern Ukraine", the statement added.
Washington says Russia is providing the separatists with military equipment, including tanks, and is building up troops on its border with Ukraine.
Moscow denies the claim.
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