UKRAINE has said a missile which downed a Ukrainian transport plane near the border was probably fired from Russia as Kiev claimed Moscow was once more massing troops on the frontier
President Petro Poroshenko held an emergency meeting of his security chiefs after a weekend of Ukrainian air strikes on rebel positions near the border with Russia and charges by Moscow that Kiev killed a Russian man with a cross-border shell.
The war of words between Kiev and Moscow and intense fighting, in which Ukrainian forces say they inflicted heavy losses on the rebels, marked a sharp escalation in the three and a half month conflict in which several hundred Ukrainian servicemen, civilians and rebels have been killed.
Mr Poroshenko said information had been received that Russian staff officers were taking part in military operations against Ukrainian forces.
He made similar complaints of Russian incursions on Sunday to the European Union with an eye to pushing the bloc to exert greater pressure, and possibly more sanctions, on Moscow.
The Ukrainian president also told his security chiefs government forces, which lost 23 men in a rocket attack on an army camp last Friday, were now facing a new Russian missile system and there would have to be a change in tactics.
Nato said Russia had increased its forces along the border and now had 10,000-12,000 troops in the area.
Ukraine's defence minister said a Ukrainian AN-26 transport plane, taking part in the military campaign against the rebels, had been shot down by a rocket which was "probably" fired from Russian territory.
Officials said crew members had been in contact with the army general staff. There was no word on casualties.
Until the weekend escalation in tension, Russian President Vladimir Putin had appeared intent on disengaging, pulling back tens of thousands of troops he had massed at the frontier in the face of threats of further sanctions.