The announcement came after several groups of Russian volunteers fighting for Ukraine said they had crossed the border in the region of Kursk in western Russia.

The defence ministry said that Russian forces "thwarted an attempt by the Kyiv regime to make a breakthrough into the border territory of the Russian Federation in the Belgorod and Kursk regions".

It said the first attempt began at 3:00 am local time (00:00 GMT) in the Belgorod region but that the Russian military and the Federal Security Service beat back the attacks.

It claimed without providing evidence to have destroyed dozens of Ukrainian servicemen as well as several armoured vehicles.

A second attempt started approximately three hours later in the neighbouring region of Kursk, also bordering Ukraine, the defence ministry said.

"Having suffered significant losses, the enemy was driven back," the defence ministry said in its statement.