NATO is concerned about convoys of trucks taking artillery and supplies into east Ukraine from Russia, and wants to see international borders respected, the supreme allied commander said Tuesday.
Ukraine responded to a report on Sunday by the Organization for Security and Cooperation in Europe, or OSCE, by accusing Russia of sending a column of 32 tanks and truckloads of troops to help the pro-Russian rebels who hold two enclaves of eastern Ukraine.
Moscow has long denied repeated accusations that its troops are operating in east Ukraine, although many have died there, and neither the OSCE nor NATO's commander, U.S. Air Force General Philip Breedlove, accused Russia by name.
"Material, equipment, armored weapons, supplies continue to flow into eastern Ukraine. More have been seen in the past several days," Breedlove told journalists at a NATO base near Naples.
"I am concerned about the increased movement."
He urged parties to the conflict "to return to norms that we expect in Western civilization: that nations will respect international borders."
The OSCE said it had spotted an unidentified armored column in rebel territory carrying uniformed troops without insignia. Kiev said these were Russian reinforcements being sent to protect the enclaves that the Kremlin now refers to as "New Russia."
A two-month-old cease-fire intended to end a war that has killed 4,000 people has appeared increasingly shaky over the past week, and Breedlove said it was a cease-fire "in name only."
"The violence continues to increase day by day," he said, adding that the number of Russian troops inside east Ukraine who were helping and training rebel forces to use sophisticated weaponry had probably risen from earlier estimates of 250-300.
Breedlove also said Russia continued to keep about eight battalions of troops on Ukraine's border, and had moved forces capable of delivering nuclear weapons to the Crimea region, which Russia annexed from Ukraine in March.
"Whether they are (nuclear) or not, we do not know," he said.
Breedlove said the number of close air, land and sea encounters between Russian and NATO forces had risen sharply:
"In the air those interactions have multiplied, by some accounts, as many as three times ... We now see larger (Russian) forces participating, as opposed to one or two bombers in the past," he said.