Sri Lanka's police Friday suspended three officers over an assault against an autistic teenager after CCTV footage shared on social media triggered protests calling it a racially-motivated attack.

The 14-year-old boy from the minority Muslim community had been stopped at a checkpoint at the southern town of Aluthgama where police allegedly beat him up for violating a curfew last week. The coastal town of Aluthgama, south of Colombo, is a flashpoint for inter-communal unrest. Three Muslims were killed during mob violence blamed on Buddhist nationalists in June 2014.

Social media users criticised police after a Muslim politician, Ali Zahir Moulana, said the boy with autism spectrum disorder (ASD) was assaulted and racially abused. He shared CCTV footage of the incident and said the boy was unable to communicate effectively and was on medication for his condition, which was diagnosed at the age of four.

A Sub-Inspector, a sergeant and a constable were suspended for "dereliction of duty", a police statement said adding that the assault recorded on CCTV footage was being investigated by two special units.

Five policemen and two passers-by joined in beating up Thariq Ahamed who was later tied to a post near the checkpoint until his father turned up and pleaded for his release, Moulana said. "While we raise our voices against police brutality and racial profiling in the United States, it is important that we highlight and question the rampant injustices happening within Sri Lanka as well," Moulana said.

He said a judicial medical officer who examined the teen had made derogatory remarks about minority Muslims in the majority Buddhist nation and also accused them of spread the coronavirus. Moulana's social media posts attracted reactions from both ruling party and opposition politicians who called for an investigation.

Prime Minister Mahinda Rajapaksa's former legislator son Namal said he "strongly condemned" those involved in the "abuse of Thariq Ahamed" and urged a full inquiry. "It's sad that the excellent work done by police during the #COVID19SL pandemic is now questioned after this," Rajapaksa said on Twitter.

For its part, police in a previous statement admitted they used force to "control the suspect as he tried to escape" but denied assaulting him. In their defence, police said Friday that they initially suspected Ahamed to be a drug addict and was unaware of his medical condition.

Police said the teen had been taken before a Judicial Medical Officer (JMO) and a report was awaited. Two separate investigations were under way, the police statement said. Opposition politician Harsha de Silva said even a local forensic expert appeared to be prejudiced.