Pro-Russian rebels in the eastern Ukrainian town of Snizhnye raised their fists in solidarity as tanks, fitted with camouflaged protective armour, rolled past, tearing up the pavement and scaring passers-by.

The tanks drove off in a cloud of smoke to cheers from the rebels, circled one of the border town's central roundabouts and drove off to an unknown destination.

Where the tanks came from is also unknown. Whether they rolled across the border from Russia, as Ukrainian Interior Minister Arseny Avakov said, or are from a Ukrainian military stockpile, as the rebels say, is up for debate.

Regardless of the answer, the two tanks seen by Reuters correspondents this week represent the heaviest weaponry yet seen in the hands of the rebels fighting to push their self-proclaimed territories in eastern Ukraine out of Kiev's orbit.

"We got them from a military warehouse," said one of the rebels wearing a loose-fitting camouflage balaclava, as the tanks rolled out of the rebels' makeshift headquarters on the 

Any indication they came from Russia would be likely to deepen strains between Moscow and the West over the Ukraine crisis, which has caused the biggest confrontation between the Cold War-era foes since the collapse of the Soviet Union.

Kiev accuses Moscow of supporting the armed insurgency that broke out in Ukraine's predominantly Russian-speaking east after the ousting of Moscow-leaning Viktor Yanukovich as president and the installation of a pro-European government.

Avakov suggested the tanks came into Ukraine from Russia and were T-72s, one of the most commonly used tanks east of the former Iron Curtain from 1972 until the fall of the Soviet Union in 1991.

The rebels said the tanks were T-64s, a top-of-the-line fighting machine when it was first introduced eight years earlier, but in the end far too expensive for mass production.

The separatists, who arrived in the city of about 45,000 people on Saturday and had set up barricades of sandbags around the coal mine, are dismissive of a suggestion by Ukrainian President Petro Poroshenko that he may be ready for talks if the separatists lay down their arms.

"We will never put down our weapons. We will only put our weapons down under one condition, that they leave us in peace," said the balaclava-wearing member of what he called the Snizhnye people's militia. "This is our land."

Fingering the ammunition belt threaded through his Kalashnikov PKM machine gun, another rebel in visibly brand-new fatigues said: "We have enough people, enough weapons, we have fighting spirit, we have order."

The separatists denied they had any Russian citizens among their ranks, though a Reuters reporter saw rebels clad in mismatching camouflage fatigues exchanging Russian roubles for Ukrainian hryvnia currency this week.

During a government meeting in Kiev, Avakov said two tanks had been attacked after moving in the direction of rebel-controlled city of Horlivka.

"There is fighting. Part of the column was destroyed," he said. He has said the column consisted of three tanks and a number of armoured vehicles.