Chechen President Ramzan Kadyrov
Chechen President Ramzan Kadyrov is under fire for entering his sons in a cage fight to mark his 40th birthday Reuters

Russia's Sports Ministry is investigating a cage fighting competition in which three of the contestants were the pre-teen sons of Chechen strongman ruler Ramzan Kadyrov.

Kadyrov posted images of the televised event on his Instagram page, which show Ahmad, 10 , Zelimkhan, 9, and Adam, 8 taking part in the mixed martial arts (MMA) bouts in honour of the Chechen president's 40th birthday on 4 October.

Under one post, Kadyrov wrote: "Little Adam proved that he is a real lion!"

"In the final of the Grand Prix Akhmat-2016 he met David Khalatov. His opponents were strong in will and spirit, but Adam won a decisive victory and claimed the champion's belt. Congratulations Adam!" he added.

But children's rights activists, sportsmen, and politicians condemned the bouts and called for an investigation.

President of Russia's Mixed Martial Arts association, Fyodor Emelyanenko, said the bouts were "unacceptable" and that any competitors under 21 needed to wear protective gear while under 12s are banned completely from competing in MMA bouts.

"Under-twelves shouldn't even be in the audience, and here are kids of eight years old beating each other up for the amusement of adults... I deeply resent that this happened in front of the president of Chechnya," he said on social media, according to the Telegraph.

The BBC reported that Kadyrov watched the bouts sitting next to Alexander Zaldostanov, who is a political ally of Vladimir Putin and heads a nationalist biker gang called the Night Wolves.