KIEV, Ukraine — A Ukrainian military transport plane was shot down Monday along the country’s eastern border with Russia but all eight people aboard managed to bail out safely, the defense ministry said.

Separatist rebels in conflict-wracked eastern Ukraine claimed responsibility for downing the Antonov-26, but Ukrainian officials swiftly ruled that out and blamed Russia instead.

In the last two weeks, the government has halved the territory in eastern Ukraine held by pro-Russia separatists, who have been forced back into the cities of Luhansk and Donetsk. Many in the armed insurgency are known to be Russian nationals, but Moscow says they are simply citizens who went to fight in Ukraine on their own.

Defense Minister Valeriy Heletey said the plane was flying at an altitude of about 21,300 feet, which he said was too high to be reached with the weapons used by the separatists. Rebels are known to have Igla portable surface-to-air missiles, which work at lower altitudes.

Ukraine’s Security Council spokesman Andrei Lysenko said data from the plane’s crew suggested the rocket was either a surface-to-air Pantsir missile or a missile fired by a plane from Russia’s Millerovo Air Force base.

Fighting intensified around Luhansk, meanwhile, as government forces stepped up efforts to disrupt rebel lines and reclaim more territory.

The Defense Ministry said Monday that government troops had retaken several villages around Luhansk and had reopened a corridor to its civilian airport. Those areas are north, west and south of the city, suggesting the government’s plan to form a security cordon around Luhansk is yielding results.