Sri Lanka widened a curfew after attacks on mosques and Muslim-owned businesses in the worst unrest since Sri Lanka bombings by Islamist militants and blocked Facebook and WhatsApp to stop people inciting violence.

The island nation has ramped up security as fears grow that minority Muslims among its population of 22 million could face sectarian violence after Islamist bombers blew themselves up in four hotels and three churches, killing more than 250 people.

Several mosques and Muslim homes were damaged in an attack overnight in the western district of Kurunegala, the Muslim Council of Sri Lanka and residents said.

Police arrested a group of men for the attacks but people in the mostly Buddhist district then demanded their release, military spokesman Sumith Atapattu said.

"To control the situation, a police curfew was imposed during the night," he said. Later on Monday, authorities extended the curfew to more villages in Kurunegala district to restore order.

Last month's bombings claimed by Islamic State have shocked the island nation of 22 million people, more than 70 percent of whom are Sinhalese Buddhists and the rest Muslims, Hindus and Christians.

Since the bombings, Muslim groups say they have received dozens of complaints about people being harassed.