Russian army tanks attacked airfields in eastern Ukraine on Monday, Ukrainian military officials said, accusing Russian army units of moving into other cities in the region and ratcheting up tensions between the two countries.

"The battle between Ukrainian paratroopers and a reinforced tank battalion of the Russian armed forces is continuing with the goal of controlling the Luhansk airfield," military spokesman Leonid Matyukhin wrote on his Facebook page.

Ukraine's Defense Minister Valeriy Geletey confirmed that Russian units are moving into other towns in the region, including the largest city of the region Donetsk. "We are fighting Russia and it is Russia which is deciding what will happen in Donbass," he told Ukraine's Inter channel late Sunday, referring to the informal name of the Donetsk and Lugansk regions.

Russian Foreign Minister Sergey Lavrov denied that Russian troops are already on the ground, saying Russia would not intervene militarily in Ukraine. 

"There will be no military intervention," Lavrov told students at Moscow State Institute of International Relations on Monday. "We call for an exclusively peaceful settlement of this severe crisis, this tragedy."

However, Ukrainian President Petro Poroshenko insisted a foreign military intervention was already underway. "Direct and open aggression has been launched against Ukraine from a neighboring state," said Poroshenko in a Monday speech at a military academy in Kiev. "This has changed the situation in the zone of conflict in a radical way."

On Sunday, Russian President Vladimir Putin called for immediate talks to set a path for statehood for the separatist region.