Ukrainian Government: Russian Military Officers Are Fighting In Ukraine As Russian Troops Crowd The Border

Ukrainian President Petro Poroshenko said on Monday Russian military staff officers were fighting against Ukrainian forces alongside separatist rebels and a new Russian missile system was being used on the separatist side.

"In the past three days a new Russian missile system has been used against the armed forces of Ukraine," he told security chiefs.

"Information has also been confirmed that Russian staff officers are taking part in military operations against Ukrainian forces," he said, according to his website.

A Ukrainian military spokesman also said on Monday that Russia is building up forces on its border with Ukraine, and separatists, backed by Russian "mercenaries", are firing on Ukrainian border guards in an attempt to bring armoured vehicles into the country.

Accusing Russia of embarking on a course of escalation in Ukraine's eastern regions, National and Security Council spokesman Andriy Lysenko told journalists:

"In the past 24 hours, deployment of (Russian) units and military equipment across the border from the Sumy and Luhansk border points was noticed. The Russian Federation continues to build up troops on the border."

In the early hours of Monday, separatists had fired on border guards and the armed forces near the border settlement of Dyakove, one of several attacks on border guards as "terrorists and Russian mercenaries" tried to bring in armoured vehicles and equipment, he said.

"The events of the last few days show that the Russian side has embarked on a course of escalation of the conflict in the Donbass," he said. Lysenko accused rebel fighters of being behind the cross-border shelling of a Russian residential area in which a Russian man was killed and which Moscow says was the work of Ukrainian forces.

"The (rebel) fighters systematically fire mortar and shoot into Russian territory which killed a Russian citizen," Lysenko said.

Russia was presenting these shooting incidents as the action of Ukrainian forces but these accusations were "absolutely unfounded," he said.

(Reporting by Natalya Zinets; writing by Richard Balmforth, Editing by Timothy Heritage)