Ukraine crisis: Government vows to punish rebels who shot down military plane, killing 49

The transport plane had 49 soldiers and crew on board when it crashed

Pro-Russian fighters walk passed the site of remnants of a downed Ukrainian army aircraft Il-76 at the airport near Luhansk, Ukraine (AP)

The Ukrainian government has vowed to retaliate after pro-Russia rebels shot down a military plane, killing 49 people on board.

President Petro Poroshenko said “terrorism” would not go unpunished and summoned security officials for an emergency summit.

Sunday was declared a day of mourning for the nine crew and 40 paratroopers who died in the most deadly single attack on government forces in the Ukrainian crisis so far.

"All those involved in cynical acts of terrorism of this magnitude must be punished," Mr Poroshenko said.

The transport plane was carrying troops and military equipment when it came under fire while coming into land in the city of Luhansk in eastern Ukraine on Saturday.

A Defence Ministry spokesman, Bohdan Senyk, said the rebels used anti-aircraft guns and a heavy machine gun to down the plane, while the prosecutor general's office mentioned an anti-aircraft missile.

Pro-Russian fighters walk passed the site of remnants of a downed Ukrainian army aircraft Il-76 at the airport near Luhansk, Ukraine (AP)

Charred debris was scattered for hundreds of metres over the sloping wheat field where the plane came down overnight near Novohannivka, a village 12 miles southeast of Luhansk.

The tail section jutted up from the ground, with parts of the engines, fuselage and other parts lying around it.

A platoon of rebel forces wearing camouflage was seen picking through the ruins for ammunition that had been intended for Ukrainian troops.

A 50-year-old rebel calling himself Pyotr said: "This is how we work. The fascists can bring as many reinforcements as they want but we will do this every time. We will talk to them on our own terms."

He had an assault rifle in one hand, a machine gun in the other and two ammunition belts round his neck.

Local residents said government forces, who control the airport, had attacked rebel positions near the airfield with jets soon after dawn.

The incident is likely to fuel tension between Russia and the United States, which accuses Moscow of arming the rebels.

Petro Poroshenko said the response would be 'adequate' (AP)

Nato released images on Saturday that it said showed recent Russian tank movements near the border.

The agency said tanks seen in Ukraine do not bear markings or camouflage paint like those used by the country’s military.

The fact they had no marks was seen as “reminiscent of tactics used by Russian elements that were involved in destabilising Crimea”.

In a sign that the separatists have increasingly powerful weaponry, they shot down a military cargo plane last week, killing three people, and a general was among 14 killed when they hit a Mi-8 transport helicopter on 29 May.

The US State Department claimed on Friday that Russia had sent tanks, heavy weapons and rocket launchers to Ukraine in recent days in support of separatists.

"We assess that separatists in eastern Ukraine have acquired heavy weapons and military equipment from Russia, including Russian tanks and multiple rocket launchers," State Department spokeswoman Marie Harf said in a statement.

She told reports that a convoy of three T-64 tanks, several MB-21 or "Grad" multiple rocket launchers and other military vehicles had crossed from Russia into Ukraine in the last three days.

"This is unacceptable," she said. "A failure by Russia to de-escalate the situation will lead to additional costs."

Evidence that Russia is sending in weapons could encourage the US and EU to impose new sanctions on Moscow, so far including visa bans and asset freezes.

The Russian government denies supporting the uprising and rebels say they get weapons from army stockpiles.

Despite the continuing violence, Ukraine and Russia have started talks on a peace plan and Moscow made a goodwill gesture by agreeing to make a last attempt to solve a gas pricing dispute before a Monday deadline to cut off supplies to Kiev.

Additional reporting by AP and Reuters