MOSCOW (AFP) - Russia said on Saturday that three shells fired by Ukrainian troops have hit a customs post and residential areas inside its territory, causing damage but no injuries.

"In the course of clashes on Ukrainian territory, the Ukrainian military fired shells which ended up on Russian territory," a spokesman for the border service in the Rostov region, Vasily Malayev, told Russian agencies.

"One seriously damaged the building of a customs post" near the border town of Gukovo while two others landed in or around nearby villages, he said.

Kiev on Friday agreed to extend until Monday a temporary truce with separatist fighters in eastern Ukraine, which borders Russia's Rostov region, however the cease-fire has been shaky at best with the rebels downing a Ukrainian helicopter earlier this week.