A Russian opposition leader has claimed that he has been attacked in a Moscow restaurant – with cake.

Former prime minister Mikhail Kasyanov told Russia's Interfax news agency that a group of men entered a restaurant in Moscow where he was dining, hurled insults at him and slammed cake in his face.

Restaurant security intervened but the men escaped in four vehicles, Kasyanov's opposition Parnas party said in a statement. Kasyanov fell out with Russian President Vladimir Putin while serving as his prime minister, and has since become a vocal critic of the Kremlin.

The restaurant incident assumes a darker light when considered alongside a recent threat made against Kasyanov by Chechen President Ramzan Kadyrov, who published a video on his Instagram page showing Kasyanov and another opposition activist targeted by rifle crosshairs. Kasyanov requested that Russian authorities investigate the video, prompting Putin's spokesman Dmitry Peskov to remark that the Kremlin did not follow Instagram.

Kasyanov told Interfax that he considered the latest attack, which he says was carried out by men of "non-Slavic appearance", a "threat to my security". Peskov responded this morning that the Kremlin considered the incident a "hooligan prank" not linked to the Chechen leadership.