Police and troops fought off hundreds of Christian-led rioters in at least six towns in North-Western Province where a curfew was imposed, police said.
"Several shops have been attacked," a senior police officer told AFP. "When mobs tried to attack mosques, we fired in the air and used tear gas to disperse them."
The curfew started in the six towns but was extended across the province amid fears that violence could spread. There were no immediate reports of casualties or arrests.
"There is a strong political element to the riots today," the police officer said. "There are people trying to make political capital out of this situation."
Earlier, authorities banned Facebook, WhatsApp and other social media platforms after overnight riots gripped several towns in the region including Chilaw. Christian groups attacked Muslim-owned shops in a sign of the heightened tensions since jihadist suicide bombers attacked three hotels and three churches on April 21 killing 258 people.
"Security forces are working tirelessly to apprehend terrorists and ensure the security of the country, but each time there is civil unrest, we increase their burden and hamper ongoing investigations."
A state of emergency has been in place since the bombings -- which the Islamic State group claims to have helped -- and security forces have been given sweeping powers to detain suspects.
"Don't laugh more, 1 day u will cry," he wrote, and local Christians took it to be a warning of an impending attack.
Sri Lanka has been on high alert since the Easter Sunday attacks
businesses were also attacked.
A curfew was imposed until dawn Monday and reimposed after a 10-hour break.
There have already been clashes between Christians and Muslims in Negombo, the town north of Colombo that was targeted by the suicide attackers.
The main body of Islamic clerics, the All Ceylon Jamiyyathul Ulama (ACJU), said there was increased suspicion of Muslims after the Easter Sunday attacks.
"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.
Internet service providers said they have been instructed by the telecommunications regulator to block access to Facebook, WhatsApp, YouTube and Instagram.
The latest unrest came as Catholic churches resumed public Sunday masses for the first time since the bombings.
Worshippers were searched before being allowed into churches that were guarded by armed police and troops. There were no reports of disruption to services, however.
Public schools completed their reopening from extended Easter holidays after the attacks, but attendance was extremely low, according to education authorities.
Private Catholic schools were to open on Tuesday, but many plan to stay closed until next week, parent groups said.
Muslims make up around 10 percent of Buddhist-majority Sri Lanka's 21 million population and Christians about 7.6 percent.
- Mosque attack -
Police said a mob targeted Muslim-owned shops in Chilaw on Sunday in anger at a Facebook post by a shopkeeper."Don't laugh more, 1 day u will cry," he wrote, and local Christians took it to be a warning of an impending attack.
Sri Lanka has been on high alert since the Easter Sunday attacks
businesses were also attacked.
A curfew was imposed until dawn Monday and reimposed after a 10-hour break.
There have already been clashes between Christians and Muslims in Negombo, the town north of Colombo that was targeted by the suicide attackers.
The main body of Islamic clerics, the All Ceylon Jamiyyathul Ulama (ACJU), said there was increased suspicion of Muslims after the Easter Sunday attacks.
"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.
Internet service providers said they have been instructed by the telecommunications regulator to block access to Facebook, WhatsApp, YouTube and Instagram.
The latest unrest came as Catholic churches resumed public Sunday masses for the first time since the bombings.
Worshippers were searched before being allowed into churches that were guarded by armed police and troops. There were no reports of disruption to services, however.
-Schools reopen -
Dozens of people have been detained since the Easter Sunday attacks. Amid the heightened security, students are only allowed into schools after checks for explosives.Public schools completed their reopening from extended Easter holidays after the attacks, but attendance was extremely low, according to education authorities.
Private Catholic schools were to open on Tuesday, but many plan to stay closed until next week, parent groups said.
Muslims make up around 10 percent of Buddhist-majority Sri Lanka's 21 million population and Christians about 7.6 percent.
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