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 on Tuesday.
East Ukraine's rebel stronghold Donetsk was pummeled on Sunday by the heaviest shelling in a month, and the OSCE said it spotted an armored column of troops without insignia in rebel territory that Kiev said proved Moscow had sent reinforcements.
U.S. Secretary of State John Kerry said on Saturday that the United States and Russia had agreed to exchange information about the situation on the Russia-Ukraine border.
Ukraine's military accused Russia on Friday of sending a column of 32 tanks and truckloads of troops into the country's east to support pro-Russian separatists fighting government forces.
