AFP
Ukraine and the West said Thursday that Russian troops were actively involved in the fighting tearing apart the east of the country, raising fears of a direct military confrontation between Kiev and its former Soviet master.
The UN Security Council geared up for an emergency meeting on the crisis as the latest rapid-fire developments sent alarm bells ringing in the United States and Europe.
Ukrainian President Petro Poroshenko held an urgent meeting with his security chiefs after scrapping a visit to Turkey over what a top official described as a "direct invasion" by Russia.
NATO said at least 1,000 Russian troops were on the ground supporting pro-Kremlin separatists who have been fighting against Kiev's rule since April, but Moscow insisted none of its soldiers were on Ukrainian soil.
US officials accused Russian troops of being behind a lightning counter-offensive that has seen pro-Moscow rebels seize swathes of territory from government forces, dramatically turning the tide in the four-month conflict.
"I will be frank, the situation is extremely difficult," Poroshenko told security chiefs.
"But it is manageable, manageable enough for us not to panic, keep a cool head, good sense and continue calculating our actions," he said.
Kiev said Russian soldiers had seized control of a key southeastern border town and a string of villages in an area where fighting had been raging for days.
"An increasing number of Russian troops are intervening directly in fighting on Ukrainian territory," the US ambassador to Kiev Geoffrey Pyatt wrote on Twitter.
A NATO official said the supply of weapons to the rebels had also increased in both "volume and quantity".
But Russia swiftly denied the allegations, with its envoy to the OSCE pan-European security body insisting: "There are no Russian soldiers in eastern Ukraine."
Britain warned Russia it could face "further consequences" as EU leaders are due to discuss the crisis on their doorstep at a weekend summit.
