NATO chief Anders Fogh Rasmussen told Russia on Friday to halt its "illegal" military actions in Ukraine.

NATO chief Anders Fogh Rasmussen told Russia on Friday to halt its "illegal" military actions in Ukraine.

"We condemn in the strongest terms Russia's continued disregard of its international obligations," Rasmussen said after an emergency meeting of the alliance on the crisis.

"We urge Russia to cease its illegal military actions, stop its support to armed separatists, and take immediate and verifiable steps towards de-escalation of this grave crisis."

Rasmussen also said NATO was not closing the door to Ukraine's possible membership of the transatlantic alliance after the government said it wanted to join.

Russian President Vladimir Putin demanded on Friday that the Ukrainian government hold "substantial" talks with the pro-federalization fighters.

"I believe that what is happening in Ukraine right now is in principle our common colossal tragedy and it is necessary to do everything for it to stop as soon as possible," he said.