The defense minister on Wednesday urged volunteer battalions involved in the government's military operation in eastern Ukraine to join the Armed Forces as its formal units as soon as possible.

"The activities of any armed unit must be based on law. Therefore, I call upon all the volunteers to make their choice as soon as possible and join the military of the country: the future of our nation depends on this," Poltorak said in a statement posted on his ministry's website.

"The leadership of the Ministry of Defense of Ukraine and the personnel of the Armed Forces of Ukraine have great respect for the courageous fighters of the volunteer battalions, who have risen to the defense of their country. Their selflessness and motivation are unquestionable," Poltorak said.

"Only by unifying to form a single powerful force will be able to effectively repel any enemy that decides to encroach upon the freedom and territorial integrity of Ukraine," he said.