Military plane shot down by rocket in eastern Ukraine as fighting intensifies

A Ukrainian military transport plane was shot down Monday along the country's eastern border with Russia as fighting between government forces and pro-Russian rebels intensified.

The Ukrainian military stepped up efforts to retake more territory in the city of Luhansk from the weakening insurgency, the Ukrainian Defense Ministry said Monday. Government defense officials said their troops have taken control of several villages on the fringe of Luhansk and reopened a corridor to the airport.

Luhansk resident, Sergei -- who declined to give his last name due to fears of reprisal -- told the Associated Press that panic had gripped the city Monday after reports that Ukrainian paratroopers were intermittently entering the city center and detaining rebel fighters. Exit points from the city have been blocked and militiamen are confiscating cars and belongings from residents attempting to flee, Sergei said.

Rebels immediately claimed responsibility for downing an Antonov-26 plane, but Ukrainian Defense Minister Valeriy Heletey said the rocket may have been fired from Russia.

Heletey said the plane was flying at an altitude of 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 the plane may have been carrying around 20 people, but there was no immediate word on casualties.

In the last two weeks, the Ukrainian government has halved the territory held by pro-Russia separatists, who have been forced back into strongholds around the cities of Luhansk and Donetsk. Those two mostly Russian-speaking regions have declared independence from the government in Kiev.

Meanwhile, NATO reported a significant increase in Russian troops along the Ukrainian border Monday.

Russia withdrew most of the 40,000 troops it had close to the Ukrainian border earlier this year, reducing them to fewer than 1,000 by mid-June. But since then, it has been building up its forces again, a NATO military officer -- speaking on condition of anonymity -- told Reuters Monday.

``Our current assessment is that between 10,000 and 12,000 troops are now in the area ... In the last week alone, we have seen several units moving into the border region,'' the officer said.

The government in Kiev has insisted that the separatists are receiving substantial manpower and military equipment from Russia, a charge Russia has always denied.

"In the last three days, Ukraine's armed forces have been attacked with Russian multiple-rocket launchers," President Petro Poroshenko said Monday at a meeting of his security officials.

Poroshenko announced he has more evidence that Russia has directly supported a separatist insurgency against his government that is dragging into its fourth month, but did not elaborate.

Ukraine maintains it’s reclaiming its territory from the rebels. "Due to successful offensives by forces in the Donetsk region, some militants are trying to leave the city," the Defense 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, 6 miles west of the airport. She says at least three Ukrainian soldiers were killed in that clash.

The Associated Press contributed to this report.