KIEV The Ukrainian military said on Monday a group of Russian forces, in the guise of separatist rebels, had crossed into south-east Ukraine with ten tanks and two armoured infantry vehicles, aiming to open a new front in the separatist war.
Earlier, a separate military statement said border guards had halted the armoured column outside Novoazovsk, Ukraine's most south-easterly point on the Azov Sea, and local residents, reached by phone, spoke of seeing tanks and other armoured vehicles moving near the town.
"This morning there was an attempt by the Russian military in the guise of Donbas fighters to open a new area of military confrontation in the southern Donetsk region," spokesman Andriy Lysenko told journalists.
Donbas is the local name given to the industrialised east that has been the scene of a five-month conflict.
If the rebels seized control of the southern regions, they could support the separatist stronghold city of Donetsk from the south with easier access to the Russian border.
Fighting between government forces and pro-Russian separatists has been hitherto concentrated around the two big rebel-held cities of Donetsk and Luhansk.
Ukraine has accused Moscow of carrying out regular cross-border shelling of government positions to shore up the rebels who have been increasingly hemmed in by Kiev's forces.
It has also charged Russia with carrying out cross-border incursions involving Russian military to carry out operations in support of the rebels. Moscow denies these charges.
The fresh charges of a blatant Russian military incursion into Ukraine is certain to sour further the atmosphere between the two powers ahead of talks on Tuesday between Ukrainian President Petro Poroshenko and Russia's Vladimir Putin.
The talks in the Belarussian capital of Minsk, which will also involve top European Union officials, will produce the first encounter since June between the two leaders.
But with Russia blaming the crisis on Ukraine's military offensive and Ukraine refusing to show restraint until Russia halts its support for the rebels the chances of any breakthrough appear slim.
The new military thrust - whether it is by separatist rebels alone or with the aid of Russian soldiers - might be aimed at capturing Mariupol, a key government-held port city on the Azov Sea.
But Lysenko said the main highway linking Novoazovsk to Mariupol, about 30 km west along the coastline, was still under the control of government forces.
"Novoazovsk has not been seized. The highway is under the control of forces of the anti-terrorist operation. We have enough resources in Mariupol itself to repel any attacks," he said.
The commander of a Ukrainian national guard unit in the area near Novoazovsk where the fighting was reported to be happening told Reuters by telephone: "A war has broken out here." He said he could not speak and ended the conversation.
Semen Semenchenko, commander of the pro-government Donbas militia, on his Facebook page gave a different version of events, saying that around 50 armoured vehicles had crossed the border from Russia.
About 40 of them were trying to move in the direction of Mariupol while the remainder were moving north towards Amvrosiyivka, he said.
"The invasion of the Russian occupiers is taking place," he said. The attacking forces were, for now, "localised and easily neutralised" and there had been no fighting yet around Mariupol itself, he added.
The column's movement towards Novoazovsk had been accompanied by artillery shelling from across the border, he said.
Lyudmila, a resident of Novoazovsk who was reached by telephone, said: "Everything began at 8 o'clock this morning. Tanks appeared - no fewer than 7 of them, and Grads (rockets) and armoured vehicles."
She said some of the tanks bore flags with emblems of a separatist group calling itself the Orthodox Liberation Army.
She said the rebel forces had fired on Novoazovsk from the village of Markine, about 7 kms away.
"Novoazovsk has died. People are hiding (from the shelling). We heard rumours of an invasion just a couple of days ago. The Ukrainian flag has been taken down on the city council offices," she said.
Asked at a news conference in Moscow about reports of an incursion across the border from Russia into the area of Ukraine near Markine, Russian Foreign Minister Sergei Lavrov said: "I have not heard of this, but there is plenty of disinformation out there about our 'incursions'."
The separatist rebellions erupted in Ukraine's mainly Russian-speaking east in April after street protests ousted a Moscow-backed president in February.
When leaders with a pro-Western agenda took power in Kiev, Russia annexed Crimea and Putin spoke of Russia's right to defend the interests of Russian-speakers in Ukraine.
The United Nations say more than 2,000 people - Ukrainian service personnel, civilians and rebels - have been killed in the conflict.
The Ukrainian military said on Sunday that the total number of Ukrainian forces killed stood at 722, though Lysenko said on Monday that four more service personnel had died in the past 24 hours.