Ukrainian forces are hunting for the crew of a downed military plane after Kiev said the aircraft was “likely” shot down from Russia, ratcheting up tensions along their volatile border.

“Crew members from an AN-26 plane … that was shot down have established contact with the general staff,” said a statement on the Ukrainian presidency website, without giving further details on the whereabouts of the eight people on board.

It said the transport aircraft had been flying too high to be hit by portable missile systems used by the rebels, meaning the shots had come “likely from the territory of the Russian Federation”.

A spokesman for Ukraine’s National Security and Defence Council said they thought the plane was hit either by a Greyhound surface-to-air missile or a projectile fired from a jet that had taken off in Russia.

An AFP crew found the wreckage of the plane strewn around a field in the rebel-controlled eastern Lugansk region close to the border with Russia and local residents said it had come down shortly after midday with some parachutes spotted in the sky.

Ukrainian military spokesmen said they had been in touch with two crew members and an AFP journalist said that charred human remains were visible amid the detritus of the crash.

Rebels claimed their fighters had shot down the craft and told Russia’s Interfax news agency they had captured four crew members and were interrogating them.

Kiev’s accusation will ramp up nerves along the porous border between the two ex-Soviet neighbours – with NATO accusing Russia of upping troop numbers on the frontier from less than 1000 to as many as 12,000.

Tensions had already soared after a shell reportedly from the Ukrainian side killed a Russian civilian on Sunday.

The foreign ministry in Moscow warned that Kiev risked “irreversible consequences”.

The ministry said on Monday it was inviting international observers from the Organisation for Security and Cooperation in Europe (OSCE) to monitor the border as a “goodwill gesture”.

Kiev has denied that its forces were behind the shelling.

The downing of the aircraft came as Ukrainian forces claimed to be making gains around the key rebel stronghold of Lugansk.

An AFP journalist saw the burned-out wreckage of three unidentified armoured vehicles along the road to the airport and later heard explosions and plumes of black smoke close to the town Monday afternoon.

Lugansk is the capital of one of the rebels’ two self-declared “People’s Republics” and – along with million-strong Donetsk – now finds itself in the crosshairs of Kiev’s reinvigorated military push to quash the three-month insurgency tearing apart the ex-Soviet state.

Local authorities said three people were killed and 14 wounded in various incidents around the city over the last 24 hours.

The conflict has now claimed some 550 lives.