The Ukrainian military said Monday it was fighting a column of armored vehicles that recently crossed the Russian border into southeast Ukraine.
It added the vehicles of the pro-Russian separatist movement were stopped at the town of Novoazovsk, on their way to a purported opening of a second front at the southeastern city of Mariupol.
The majority of the fighting between the Ukrainian military and rebels thus far has been in the northeastern part of Ukraine.
The claim comes a day before Ukrainian President Petro Poroshenko and Russian President Vladimir Putin are scheduled to hold a one-day summit meeting in Minsk, Belarus. Military spokesman Col. Andriy Lysenko said 10 tanks, two armored vehicles and two trucks crossed the border; various witnesses claimed they saw between 10 and 30 vehicles.