KIEV — 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.
There was no immediate comment from Russia on the matter.
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 up to about 11,500 feet.
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.
In London, Charles Heyman, a defense analyst who edits a book called ‘‘Armed Forces of the European Union,’’ said the missile was more likely fired by the Ukrainian rebels.
‘‘I doubt the transport plane was flying at 6,500 meters. That doesn’t make sense. The higher you fly, the more it costs, and the plane would have had to be pressurized,’’ Heyman said. ‘‘It was probably shot down using SAM-6 missiles owned by the rebels, which they have quite a few of.’’
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 —including Metalist, Oleksandrivsk, Bile, and Rozkishne — 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.
One Luhansk resident said that panic had gripped the city Monday over reports that Ukrainian paratroopers were slipping in and detaining rebel fighters. Exit points from the city have been blocked and militiamen were confiscating cars and belongings from residents attempting to flee, he said.
A spokeswoman for the separatist Luhansk People’s Republic said that they destroyed a Ukrainian armed convoy in the village of Heorhiivka, killing at least three Ukrainian soldiers.
It was not possible to immediately verify the claim.
Ukraine’s authorities insisted again that Russia was directly supporting the separatist insurgency now dragging into its fourth month.
‘‘In the last three days, Ukraine’s armed forces have been attacked with Russian multiple-rocket launchers,’’ Ukraine’s president, Petro Poroshenko, said Monday at a meeting with top security officials.
Moscow in turn accuses Ukraine of spreading the unrest to its own territory. Russian media reported Sunday that a Ukrainian shell had hit a building in a Russian border town, killing one person and seriously injuring two.
Ukraine denied that it had fired shells onto foreign soil but President Vladimir Putin expressed ‘‘grave concern’’ over the incident and Russia’s foreign ministry warned there could be ‘‘irreversible consequences.’’
Russia’s foreign minister, Sergey Lavrov, sent a letter Monday requesting that observers from the Organization for Security and Cooperation in Europe visit Russian border towns affected by the fighting. Speaking with President Didier Burkhalter of Switzerland, chairman of the European organization, Lavrov called for the resumption of talks to negotiate a cease-fire.
Ukraine’s president implemented a unilateral 10-day cease-fire but abandoned it when rebels would not lay down their arms and return captured border posts.
After a four-way telephone call with French, Ukrainian, Russian, and German officials late Monday, Foreign Minister Frank-Walter Steinmeier of Germany said all parties agreed to keep working toward a sustainable, bilateral cease-fire.
President Obama and Prime Minister David Cameron of Britain said Russia should act immediately to deescalate the situation, according to a White House transcript of a phone call between the two men Sunday.
Russia must enforce a cease-fire and halt the flow of weapons and fighters across Ukraine’s border, among other measures, Obama and Cameron said.
‘‘So far, neither the United States nor the United Kingdom have seen progress on complying with these conditions,’’ the White House said.