Christian groups threw stones at mosques and Muslim-owned shops in the northwestern Christian-majority town of Chilaw on Sunday in anger at a Facebook post by a shopkeeper, police said.

Security forces fired shots in the air to disperse mobs, but the violence spread to nearby towns where businesses owned by Muslims were also attacked.

“Social media blocked again as a temporary measure to maintain peace in the country,” Nalaka Kaluwewa, director general of the government information department, told Reuters news agency on Monday.

Police said a curfew, imposed on Sunday afternoon, in Chilaw and nearby areas was relaxed on Monday, but the social media ban was brought in to prevent incitement to violence.

“Don’t laugh more, 1 day u will cry,” was posted as a comment on Facebook by a Muslim shopkeeper, and local Christians took it to be a warning of an impending attack.

Mobs smashed the man’s shop and vandalised a nearby mosque prompting security forces to fire in the air to disperse the crowd.

Authorities said they arrested the author of the Facebook post, identified as 38-year-old Abdul Hameed Mohamed Hasmar, as well as a group of men in the nearby Kurunegala district for allegedly attacking Muslim-owned businesses.

‘Worrying trend’

Sri Lanka’s information department director told Al Jazeera that one of the main reasons behind the ban was to “clamp down on tensions and incidents that have been erupting over the last 48 hours”.

Al Jazeera’s Minelle Fernandez, reporting from the northern town of Kilinochchi, said that “the government is using this not as a long-term measure, but as a tactic to dampen any tensions that might erupt”.

Sri Lankah has been on edge since the April 21 attacks by Muslim suicide bombers on three hotels and three churches that killed at least 257 people.

Muslims make up around 10 percent of Buddhist-majority Sri Lanka’s 21 million population and Christians about 7.6 percent.

Rights group Amnesty International said there was “a worrying trend of attacks against the Muslim community coming out of Sri Lanka” following the Easter Sunday bombings.

The main body of Islamic scholars, the All Ceylon Jamiyyathul Ulama (ACJU), said there was increased suspicion of Muslims.

“We call upon the members of the Muslim communities to be more patient and guard your actions and avoid unnecessary postings or hosting on social media,” the ACJU said.

Sri Lanka has used temporary bans on social media in a bid to deter misinformation and rumours.

On Twitter, Sri Lanka’s leading mobile phone operator Dialog said it had also received instructions to block Viber, IMO, Snapchat, Instagram and Youtube until further notice.

Sri Lanka has been under a state of emergency since the attacks. Security forces and police have been given sweeping powers to arrest and detain suspects for long periods.