LUGANSK, Ukraine: Pro-Russian gunmen shot down a Ukranian military transport plane Saturday in the separatist east, killing all 49 people on board in the biggest single loss of life in the two-month insurgency.
The early morning downing near the airport of the rebel stronghold city of Lugansk came a day after Ukrainian forces notched their biggest success of their deadly campaign to reunify the splintered nation by reclaiming control of a strategic southeastern industrial port.
The United States on Friday accused Russia of helping in the insurgency by sending tanks and rocket launchers to the pro-Moscow rebels, a charge denied by the Kremlin.
Closed-circuit camera footage of the downing showed a small flash flare in the sky when the large Il-76 plane was hit by what Ukrainian officials said was heavy-calibre machinegun fire.
A massive second burst of light lit up the horizon when the plane apparently exploded upon hitting the ground while approaching the Lugansk airport.
"The terrorists cynically and treacherously fired with a large-calibre machinegun hitting an Ilyushin-76 of the Ukrainian air force which was carrying troops on rotation and was about to land at Lugansk airport," the ministry said in a statement.
A spokesman for Ukraine's self-proclaimed "anti-terrorist operation" said the plane was carrying nine crew members and 40 paratroopers.
"They all died," spokesman Vladyslav Seleznyov told AFP by telephone.
The four-engine jet was also carrying military equipment.
An AFP correspondent heard heavy fighting and a series of loud explosions in the hours preceding the downing in Lugansk, a city of 400,000 lying just 25 kilometres (15 miles) west of the Russian border.
The city has been under effective rebel control since the eastern uprising began in early April, but Ukrainian forces had managed to hold on to its airport and use it to rotate troops serving in the campaign.
But they have been forced to repel an increasingly frequent series of raids on the air hub by the gunmen, who had also briefly seized the main international airport in the neighbouring rebel-held city of Donetsk at the end of May.
The two-month insurgency is now known to have claimed at least 320 lives of civilians and fighters on both sides.
The United States on Friday accused Russia of sending tanks and rocket launchers to the rebels in the wake of Western-backed tycoon Petro Poroshenko's victory in May 25 presidential elections.
"We are highly concerned by new Russian efforts to support the separatists," deputy spokeswoman Marie Harf said.
Poroshenko had told his Russian counterpart Vladimir Putin on Thursday that the tanks' crossing into Ukraine was "unacceptable".
Russia called the tanks reports "disinformation", but Washington backed Kiev's claims, saying that the separatists had also obtained multiple rocket launchers from Russia among other heavy weapons and military equipment.
NATO chief Anders Fogh Rasmussen warned that reports of pro-Russian groups acquiring heavy weapons from Russia, including tanks, would mark a "serious escalation" of the crisis if confirmed.
Poroshenko had on Friday celebrated the "heroism" of soldiers hoisting the national flag over the strategic rebel-held port of Mariupol.
He proclaimed the industrial Sea of Azov city the new temporary capital of Donetsk -- an eastern rustbelt region overrun by pro-Russian gunmen for the past two months.
Mariupol has wavered between rebel and Kiev control for weeks and was also the scene of pitched battles on May 9 that killed more than a dozen people.
Monday morning gas cut
Poroshenko's troubles have been compounded by the threat of Ukraine being cut off from economically-vital Russian gas shipments as early as Monday morning because of a bitter price dispute.
Prime Minister Arseniy Yatsenyuk told regional administrations and the heads of the state energy company to prepare for the consequences of a possible gas cut by implementing a plan for reduced energy use.
Ukraine receives half its gas supplies from Russia and transports 15 percent of the fuel consumed in Europe.
The head of Ukraine's state energy firm said Kiev was ready to make a $1.95-billion (1.45-billion-euro) payment demanded by Moscow by Monday if Russia settled on a price of $326 per 1,000 cubic metres of gas.
European Commission chief Jose Manuel Barroso meanwhile told the Russian leader he was willing to include Moscow in discussions with Kiev weeks before the EU is due to sign an association accord and free trade pact with the former Soviet state. (AFP)