Updated

A human rights group has expressed concern over rising brutal attacks in India by self-appointed "cow protectors" against Muslims and lower castes over rumors that they sold, bought or killed cows for beef.

Human Rights Watch said Friday that Indian authorities should promptly investigate the attacks prosecute those responsible. Many critics allege the vigilantes are linked to extremist Hindu groups affiliated with the ruling Bharatiya Janata Party.

Human Rights Watch says that since Prime Minister Narendra Modi's government came to power in 2015, at least 10 Muslims have been killed in mob attacks related to allegations over cows. Modi has condemned the attacks.

Eighty percent of India's 1.3 billion people are Hindu, who consider cows to be sacred. The selling of beef is banned in several Indian states.