CNN reports that Pro-Moscow rebel forces in eastern Ukraine, backed by Russian tanks and armored personnel carriers, battled government forces on two fronts Thursday, a Ukrainian military official said.

The fighting was taking place southeast of Donetsk, and along the nation's southern coast in the town of Novoazovsk, about 12 miles (20 km) from the Russian border, according to Mykhailo Lysenko, the deputy commander of the Ukrainian Donbas battalion.

"This is a full-scale invasion," Lysenko said, referring to the fighting in the south.

"There is military equipment in Novoazovsk which came across the border two days ago from Russia," the fighter, from the so-called Azov battalion which supports the Ukrainian army, told Reuters by telephone.

"The equipment is carrying the flags of the DNR (Donetsk People's Republic) rebels but they are regular Russian forces," the fighter who did not wish to be identified by name, said.

Separately, a resident of the town on the Sea of Azov, who would only give his first name of Mykola, said: "The authorities in the town are DNR ones. Tanks are moving here and there out on the highway, but there is no fighting going on for the town."

In a Cabinet meeting Thursday, Ukraine's Prime Minister, Arseniy Yatsenyuk, called for an immediate U.N. Security Council meeting.

"Russia has very much increased its military presence in Ukraine," he said.

U.S. Ambassador to Ukraine Geoffrey Pyatt also said Thursday that Russian soldiers were directly involved in the fighting, alongside the pro-Russia rebels.

"Russian supplied tanks, armored vehicles, artillery and multiple rocket launchers have been insufficient to defeat Ukraine's armed forces, so now an increasing number of Russian troops are intervening directly in the fighting on Ukrainian territory," he said on Twitter.

"Russia has also sent its newest air defense systems including the SA-22 into eastern Ukraine and is now directly involved in the fighting."

Moscow denies supporting and arming the pro-Russia rebels. It has also repeatedly denied allegations by Kiev that it has sent troops over the border.

Yatsenyuk suggested tougher measures may be needed to curb Russia's support for the rebels.

"Unfortunately, the sanctions were unhelpful as to deescalating the situation in Ukraine," he said, referring to the economic sanctions already imposed by the United States and European Union against Russian individuals and companies.

Yatsenyuk suggested one way to halt "Russian aggression" could be to freeze all assets and ban all Russian bank transactions until Russia "pulls out all its military, equipment and agents" from Ukraine.

"Vladimir Putin has purposely started a war in Europe. It is impossible to hide from the fact," he said.

In a foreign policy address in Paris, French President Francois Hollande said that if there's evidence that Russian soldiers are on Ukrainian soil "it would be intolerable and unacceptable."

NATO officials are due to give a briefing Thursday on the situation in Ukraine.
U.S. State Department spokeswoman Jen Psaki on Wednesday highlighted the latest reports of heavy fighting around Novoazovsk and Donetsk airport, as well as of "additional columns of Russian tanks, multiple rocket launchers and armored vehicles" heading for communities in southeastern Ukraine.

"These incursions indict a Russian-directed counteroffensive is likely underway in Donetsk and Luhansk," she said. "Clearly that is of deep concern to us."

She accused Moscow of not acting in a transparent manner when it came to the Russian people, as well as Ukraine and the rest of the world.