Russia said one of its border checkpoints in south Rostov region was hit Thursday by mortar shells from Ukraine, with no casualties reported.

"The shells hit Russian territory at Novoshakhtinsk checkpoint at about 5:30 a.m. Moscow time (0130 GMT)," Itar-Tass news agency quoted a spokesman of the Rostov regional Federal Security Service as saying.

Vasili Malayev said the shells also hit a coach station and customs cargo terminal nearby, adding the checkpoint has been temporarily closed.

The spokesman did not say who was behind the shelling, but the Ukrainian Border Service said separatists in the country were to blame for the incident.

On Wednesday, Ukrainian National Security and Defense Service (SNBO) confirmed that Russia had closed three border-crossing points since Tuesday.

"Russia closed checkpoints at Gukovo, Donetsk and Novoshakhtinsk in Rostov region which the rebels used for crossing the border," the Unian news agency quoted SNBO spokesman Andrei Lysenko as saying.

The SNBO has obtained information that Russia has been trying to prevent the armed insurgents from self-proclaimed Donetsk and Lugansk republics to sneak into Russian territory through these checkpoints, Lysenko said.

On June 21, over 80 Ukrainian border guards found refuge on the Russian side of the border at the Izvarino-Donetsk checkpoint after fleeing from armed anti-government insurgents. Most of them later returned to Ukraine.