BRUSSELS

 NATO Secretary General Jens Stoltenberg has again urged Russia to withdraw what he claimed were its forces from eastern Ukraine amid fierce fighting in the embattled town of Debaltseve.

His comments came on Wednesday as Ukrainian President Petro Poroshenko said government forces were withdrawing from the key eastern town of Debaltseve.

Speaking at an informal EU defense ministers meeting in the Latvian capital of Riga on Wednesday, Stoltenberg told reporters: "I urge Russia to withdraw all its forces form eastern Ukraine, to stop all its support for separatists and to respect the Minsk agreement."

EU Foreign Policy chief Federica Mogherini said in a statement: "The actions by the Russia-backed separatists in Debaltseve are a clear violation of the ceasefire."

"The separatists must stop all military activities. Russia and the separatists have to immediately and fully implement the commitments agreed to in Minsk."

- Claims rejected

Poroshenko said 80 percent of Ukrainian forces had pulled out of Debaltseve - a key transport hub which both separatists and government forces have fought hard to control - and more were preparing to leave.

Russia has repeatedly rejected claims it is directly involved in the fighting in eastern Ukraine, while local media has reported rumors that U.S. private military "contractors" and special forces have been engaged in the conflict.

Russian President Vladimir Putin said in late January that NATO “legions” were fighting alongside Ukrainian government troops.

Putin told students in St. Petersburg: "Who is fighting? There are official divisions of the armed forces but to a great extent there are so-called voluntary nationalist battalions.

"This is not even an army, it's a foreign legion. In this case it's a foreign NATO legion." 

More than 5,300 people have been killed and 12,200 others injured in eastern Ukraine since mid-April last year in the ongoing conflict, according to the U.N. High Commissioner for Human Rights.