A Ukrainian military transport plane was shot down Monday along the country's eastern border with Russia, the defence minister said.
Rebels in conflict-wracked eastern Ukraine immediately claimed responsibility for downing the Antonov-26 but Ukrainian Defence Minister Valeriy Heletey said the rocket may have been fired from Russia.
Heletey said the plane was flying at an altitude of 6,500 metres (21,300 feet), which he said was too high to be reached with the weapons used by the separatists fighting government troops.
Ukrainian authorities say plane may have been carrying around 20 people but there was no immediate word on casualties.
In the last two weeks, the government has halved the territory held by pro-Russia separatists, who have been forced back into strongholds around the eastern cities of Luhansk and Donetsk. Those two mostly Russian-speaking regions have declared independence from the government in Kyiv.
Fighting intensified Monday around Luhansk as government forces stepped up efforts to disrupt rebel lines and reclaim more territory from the faltering insurgency. One resident said panic was gripping the city.
Despite reports of military successes, however, Ukraine's president announced he has more evidence that Russia has directly supported a separatist insurgency against his government that is dragging into its fourth month.
The Defence Ministry said Monday that government troops had retaken several villages around the rebel-controlled city of Luhansk and had reopened a corridor to its civilian airport.
"Due to successful offensives by forces in the Donetsk region, some militants are trying to leave the city," the Defence Ministry said in a statement.
Rebels, however, insisted their fighting capabilities remain strong.
A spokeswoman for the separatist Luhansk People's Republic told The Associated Press that they destroyed a Ukrainian armed convoy in the village of Heorhiivka, 10 kilometres (6 miles) west of the airport. She says at least three Ukrainian soldiers were killed in that clash.
Government defence officials said their troops have taken control of several areas on the fringe of Luhansk — including Metalist, Oleksandrivsk, Bile and Rozkishne. Those residential areas are north, west and south of the city, suggesting the government's plan to form a security cordon around Luhansk has yielded results.
The leader of the military wing of the insurgency, Igor Girkin, also known by his nom de guerre Strelkov, had over the weekend predicted a bitter fight for Luhansk, a city of 400,000, and estimated that Ukrainian forces had deployed up to 70 tanks in the offensive.