Several dozen people threw stones at mosques and stores owned by Muslims and a local man was beaten in the town of Chilaw on Sri Lanka’s west coast on Sunday in a dispute that started on Facebook, sources told Reuters.

Three weeks ago in Sri Lanka Islamist bombers had blew themselves up in four hotels and three churches, killing more than 250 people. Since then Muslim groups say they have received dozens of complaints from across the country about people being harassed.

“A police curfew has been imposed in Chilaw Police area with immediate effect until 6 am tomorrow to control the tense situation,” police spokesman Ruwan Gunasekera told Reuters. The police later said the curfew would be lifted at 4 am.

A screenshot of the alleged Facebook exchange seen by Reuters showed a user had written in Sinhalese “It is difficult to make us cry” and added a local slur against Muslim men.

A Facebook user identified as Hasmar Hameed, whom two locals said was the man later arrested, replied in English: “Dont laugh more 1 day u will cry.”

Authorities said they arrested the author of a Facebook post.