Government forces in eastern Ukraine have begun storming the rebel-held city of Luhansk with tanks, Russian news agency reports quoting rebels say.

Heavy fighting erupted as columns of government armour attacked from the south and west, rebel military leader Igor Strelkov was quoted as saying.

He said there were unconfirmed reports of special forces landing by helicopter inside the city of 425,000 people.

There was no immediate confirmation from Kiev but bloggers report fighting.

Pro-Russian separatist rebels have been fighting the government in Kiev since declaring independence in Luhansk and the neighbouring region of Donetsk in April.

Meeting briefly in Rio de Janeiro before the World Cup final, Russian President Vladimir Putin and German Chancellor Angela Merkel agreed that the situation in Ukraine was "tending towards a deterioration", a Kremlin spokesman said.

Mr Putin expressed concern about offensive operations by the Ukrainian government, saying they were unacceptable. Earlier, Russia protested after a man was allegedly killed on its side of the border by a shell fired from Ukraine. A Ukrainian official denied the attack.

Talks in Rio between Mr Putin and Ukrainian President Petro Poroshenko were cancelled after the Ukrainian leader announced he would not be attending the final after all.

"Heavy fighting is under way on the outskirts of Luhansk," Strelkov told Ria-Novosti news agency.

"The enemy has thrown around 70 tanks into the battle in two compact groups of armour. There is as yet unconfirmed information about a helicopter landing of enemy special forces in the city itself."

(BBC)