Sri Lankan troops in a northern town fired shots into the air and police imposed a curfew on Sunday after mobs attacked a mosque, in renewed religion tensions in the wake of the Easter terror attacks.

Police spokesman Ruwan Gunasekera said that the mobs in Chilaw, 80 kilometres (50 miles) north of the capital Colombo, also attacked Muslim-owned businesses.

The violence erupted in Chilaw, a Catholic-majority town after a resident misunderstood a Facebook post as a threat against Christians.

Gunasekera said the Muslim man who posted the comment has been arrested. He said the curfew would be lifted at dawn on Monday.

The latest unrest came as Catholic churches resumed their public Sunday masses for the first time after the April 21 bombings at three churches and three luxury hotels left 258 people dead.

The attacks were blamed on a local group which had pledged an oath of allegiance to Abu Bakr al-Baghdadi, the leader of the Islamic State group.

Last week, there were similar tensions at a town between Colombo and Chilaw where an argument between two men degenerated into religious violence leaving three people wounded.

Official sources said the curfew was imposed in Chilaw to prevent the unrest spreading to other areas.

Sri Lanka has been under a state of emergency since the suicide bombings. Security forces and police have been given sweeping powers to arrest and detain suspects for long periods.

Muslims make up around 10 per cent of Buddhist-majority Sri Lanka's 21 million population and Christians about 7.6 per cent.