Police fire tear gas and water cannon at Buddhist protesters in Sri Lanka.

Bodu Bala Sena (BBS), a hard-line Sinhalese Buddhist nationalist organisation, demonstrated Monday to demand the release of their general secretary, Galagoda Aththe Gnanasara Thero.

Gnanasara is currently serving a six-year jail term, handed to him in August for contempt of court, just two months after receiving a six-month jail term for intimidation. It is highly unusual for Sri Lanka to convict Buddhist monks.

Later on Monday Sri Lankan President Maithripala Sirisena expressed regret and offered an apology to the group of protesters, according to local media.

BBS has been accused of channelling the rhetoric of populist anti-Muslim movements around the globe, and Muslims have accused BBS of stirring up violence against Muslims and Christians.

Police have fired tear gas and water cannons to disperse a group of protesters of the BBS organisation engaged in a demonstration outside the Presidential Secretariat in Colombo, Fort. The protesters were demanding the release of the General Secretary of the organisation venerable Galagodaththe Gnanasara thera. Gnanasara thera was convicted on four charges over Contempt of Court and was sentenced to a 19 year rigorous imprisonment, to be completed in 6 years.police had taken measures to control the protestors by deploying water cannons and tear gas.