Bone fragments from the sword hand of a medieval Russian prince who won a famous victory over the Mongols have been sent to the front in Ukraine to raise army morale in the Russian Orthodox Church's latest show of support for the war.

The sarcophagus of Grand Prince Dmitry Donskoy, who died in 1389 and is revered by Russian nationalists for defeating the Mongol Golden Horde at the 1380 Battle of Kulikovo, was uncovered this summer during restoration work at Moscow's Cathedral of the Archangel inside the Kremlin.

Putin personally inspected what experts said were the prince's well-preserved remains in August, hailing them as "an absolutely unique and marvellous discovery" that reinforced the foundations of Russian history.

The Russian Orthodox Church, which has backed Putin throughout the conflict, said it had dispatched a fragment of Donskoy's right hand to Donetsk, one of four Ukrainian regions Russia claims to have annexed in 2022.

Referring to Donskoy as "the holy commander," the Moscow Patriarchate of the Russian Orthodox Church said part of his remains had been sent to the front to stand invisibly shoulder-to-shoulder with Russian troops.