NATO Secretary-General Jens Stoltenberg says Russia should withdraw some 1,000 items of military equipment that it has in eastern Ukraine.
Stoltenberg, speaking after talks with Italian Prime Minister Matteo Renzi in Rome on February 26, also said any attempt by pro-Russian separatists to expand the territory they hold in eastern Ukraine would be "unacceptable."
Stoltenberg said he is cautiously optimistic the cease-fire agreed to two weeks ago between pro-Russian rebels and Ukrainian forces could be maintained.
He said he "welcome the recent indications of reduced fighting in Ukraine and we hope that the cease-fire now is finally going to be respected."
Stoltenberg said Russia has in recent months transferred more than "1,000 pieces of equipment -- tanks, artillery, and advanced air-defense systems " -- into Ukrainian territory held by the rebels.
He said Russia must "stop supporting separatists."
At least 5,600 people have been killed and hundreds of thousands have fled their homes in the fighting since April.