KIEV (Reuters) - NATO's top military commander said during a visit to Kiev on Wednesday that Russian forces were still operating in eastern Ukraine, providing the "backbone" to separatist rebels fighting government forces.U.S. Air Force General Philip Breedlove, NATO's Supreme Allied Commander Europe, also expressed concern over what he said was Moscow's militarization of the Crimea peninsula which Russia annexed from Ukraine in March.Ukraineleveled fresh charges thatRussiawas sending support to pro-Russian separatists in the east, saying that five columns of heavy equipment were seen crossing onto Ukrainian territory on Monday.The latest accusations come amid a standstill in diplomatic efforts to end the six-month conflict in the east in which theUnited Nationssays more than 4,300 people have been killed.Separately, theKiev militarysaid one soldier was killed and five others injured in the past 24 hours as a fragile ceasefire declared on Sept. 5 continued to come under pressure."The Russian side is continuing to provide the terrorist organizations of the Donetsk andLuhanskpeople's republics with heavy armaments," said a foreign ministry spokesman.Evhen Perebyinistold journalists that a total of 85 vehicles had been detected in the five columns that entered at the Izvaryne border crossing point fromRussiaon Monday."Up to six of these were heavy armored transporters. The rest were vehicles and buses carrying fighters and ammunition," he said.Despite what Kiev's pro-Western leaders andWestern governmentsay is incontrovertible proof,Russiadenies sending in troops to support separatist rebels trying to hive off parts ofUkraine's industrialized east and eventually joinRussia.Asked about reports of Russian humanitarian aid convoys enteringUkrainewithout authorization, he said: "A significant amount of the goods which are being supplied ... is fuel, ammunition and other military help."Perebyinis repeated an earlier charge that on Nov. 20, for the first time since a peace deal had been signed byRussia,Ukraineand the separatists,Ukrainehad been subjected to artillery fire from the Russian Federation near the village ofKamyshinenear the rebel-controlled border town ofLuhansk.Describing the fire as "outright aggression" againstUkraine's territorial integrity, he called onRussiato pull out its troops and equipment from Ukrainian territory.A senior Russian official said on Tuesday an announcement byUkraine's president that he would hold a referendum on NATO membership in several years' time would increase regional tensions."I am convinced that what has been announced now by the Ukrainian leadership will only bring a further escalation of the situation aroundUkraine," Interfax news agency quoted Deputy Foreign MinisterSergei Ryabkovas saying.(Editing by Timothy Heritage)Join the conversation about this story Click here to read full news..