ALUTGAMA: Sri Lanka's police arrested 49 people overnight over deadly anti-Muslim riots in a tourist region where Buddhist hardliners have set shops and homes ablaze, a senior officer said Wednesday.

Both Buddhists and Muslims were arrested during a police crackdown in the southern resort towns, where two nights of violence have left four people dead, the officer said.

“We have already arrested 49 and remanded 25 of them and further arrests will take place today,” Sri Lanka police spokesman Ajith Rohana told AFP.

A curfew was also lifted in the mainly-Muslim towns of Beruwala and Alutgama, where followers of the extremist Buddhist Force, or BBS, went on the rampage on Sunday and Monday nights.

Hundreds of troops have been deployed to help police contain the violence, which erupted after a BBS mob marched in Alutgama on Sunday, with clashes breaking out as it claimed its procession was stoned by Muslims.

Residents have said authorities did little to stop the violence, which saw dozens of shops and homes torched by mobs armed with guns, petrol bombs and knives.

The Organisation of Islamic Cooperation, one of the world's top Islamic bodies, urged authorities to investigate the violence and take action against those responsible.

OIC Secretary General Iyad Madani said he hoped “every possible effort would be exerted by the Sri Lankan authorities to prevent a further escalation of violence”.

“While appealing for calm and peaceful relations between the communities, Mr Madani urged the authorities to enforce the rule of law, investigate the incidents and bring the perpetrators to justice,” an OIC statement said.

The attacks are the latest in a series of religious clashes to hit the island following unrest in January and last year, when Buddhist mobs attacked a mosque in the capital Colombo.

Muslims make up about 10 per cent of the 20 million population, but are accused by nationalists of having undue influence in the Buddhist-majority country.

The United States has led international condemnation of the violence, while Western embassies in Colombo have advised their nationals holidaying in the area to stay indoors.