Officials told the AFP news agency the curfew was aimed at preventing an escalation of violence, after a second day of anti-Muslim riots in the country.
Two residents of Thunmodara told Reuters that a mosque and some Muslim-owned shops were attacked in the town in Kurunegala district that was hardest hit by the rioters.
Police and troops fought off hundreds of rioters in at least six towns earlier Monday with teargas.
According to the the All Ceylon Jamiyyathul Ulama (ACJU) - the main body of Islamic clerics - there has been increased suspicion of Muslims after the attacks blamed on local Islamic group National Thowheed Jamath, which is believed to have links with the Islamic State (IS) that claimed the carnage.
Prime Minister Ranil Wickremesinghe said late on Monday he had given powers to the security forces to take strong action against those responsible for anti-Muslim violence.More news: The New Stranger Things Lego Set Literally Turns Everything Upside Down
Muslims make up almost 10% of Sri Lanka's 22 million people, who are predominantly Sinhalese Buddhists.
Militant Buddhist groups have cultivated anti-Muslim sentiment in Sri Lanka for years, sparking fears soon after the Easter bombings that such groups would use the attacks as justification to incite violence against Sri Lankan Muslims.
Among those detained was Amith Weerasinghe, a man from Sri Lanka´s majority Buddhist Sinhalese community and on bail for his role in similar riots in March previous year in the central Kandy district.
"The attacks on mosques, the burning of houses and shops, the attacks on innocent people can not be condoned in any way", Jayasuriya said in a statement.
Muslims make up around 10 percent of Buddhist-majority Sri Lanka's population and Christians about 7.6 per cent. In the town of Kinyama, two mosques were smashed as outnumbered armed police and troops stood by.
"Mobs had attacked him with sharp weapons at his carpentry workshop", a police official told AFP.More news: Manchester City ‘fully co-operating in good faith’ with UEFA investigation
Ruwan Gunasekera, a police spokesman, said that more than 80 people were in custody as of Tuesday evening.
They accused the security forces and the police for becoming silent watchers to the rioting.
"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.
The government also temporarily banned social media networks and messaging apps after similar attacks in several towns on Sunday. "Social media blocked again as a temporary measure to maintain peace in the country", Nalaka Kaluwewa, the director general of the Department of Government Information said.
Communal violence in the Indian Ocean island nation has worsened in recent days, following last month's Easter Sunday bombings that killed more than 250 people.More news: HTC releases smartphone with Bitcoin full node capabilities