DHAKA (Reuters) - At least four people were killed and about 50 injured on Sunday in clashes with police in Bangladesh over a Facebook post that offended Muslims, officials said.

The clashes in the southern district of Bhola, 195 km (120 miles) from the capital Dhaka, broke out when angry crowds protested against a Facebook post in which a Hindu reportedly made derogatory remarks about Prophet Mohammad.

Police said the Facebook had actually been hacked and all the hackers had been detained.

“We fired blank shots in self-defense when some people started throwing stones at our officers forcing us to take shelter in a building,” said Sarkar Mohammad Kaisar, Superintendent of Police in Bhola.

Four people were killed and a policeman suffered bullet wounds during the clash, he said. Border guards and additional police have been sent to Bhola.