Sri Lanka has imposed a night-time curfew across the country amid an upsurge in anti-Muslim violence.
Mosques and Muslim-owned shops have been targeted but there were no reports of casualties.
In several towns, police fired into the air and used tear gas to disperse hundreds of rioters.
Tensions have been high since Islamist militants attacked churches and hotels on Easter Sunday, killing more than 250 people.
Prime Minister Ranil Wickremesinghe has appealed for calm saying the current unrest was hampering the investigation into last month’s attacks in the early hours of Monday.
The seven-hour curfew will take place from 21:00 local time (15:30 GMT).
The family networks behind the bombings
Children of the Easter Sunday carnage
Sri Lanka country profile
In the north-western town of Kiniyama, windows and doors to a mosque were smashed and copies of the Koran thrown on the floor.
The attack was triggered by a group of people demanding a search of the building after soldiers inspected a lake nearby looking for weapons, Reuters news agency reports.
In the Catholic-majority town of Chilaw, Muslim-owned shops and mosques were attacked after a dispute that started on Facebook, police said.
A 38-year-old Muslim businessman identified as the author of the post that sparked the violence was arrested.
Officials have blocked some social media platforms and messaging apps, including Facebook and Whatsapp, in an attempt to curb the violence.
“I appeal to all citizens to remain calm and not be swayed by false information”. Security forces are working tirelessly to apprehend terrorists and ensure the security of the country,” the prime minister said on Twitter, which has not been blocked.
Incidents were also reported in the town of Hettipola, where at least three shops were reportedly torched.
Muslims make up nearly 10% of Sri Lanka’s 22 million people, who are predominantly Sinhalese Buddhists.
Police have blamed two local Islamist groups for the Easter Sunday bombings. The Islamic State group has said it was involved but has given no details.
A state of emergency was declared after the attack.