COLOMBO (AFP) - Sri Lankan police were investigating a fire which on Saturday destroyed a Muslim-owned clothing store in a district where religious tensions had heightened.

The authorities had not ruled out arson at the upmarket No-Limit store in Panadura, 25 kilometres south of Colombo, police spokesman Ajith Rohana said.

"We are looking at the possibility of arson as well as an accidental fire," he told AFP. "The fire started in the upper floor and we are still investigating."

He said workers had carried out some electrical repair work the previous day.

There were six people at the store, including two unarmed guards, at the time of the pre-dawn fire, he said. The authorities tightened security in the area following the fire.

Witnesses said they heard several explosions as the fire completely gutted the two-storey building.

The fire came a day after Sri Lanka's Muslim minority held shortened Friday prayer services because of heightened religious tensions after clashes with hardline Buddhists earlier in the week in Kalutara district. The district includes Panadura and the popular and mainly Muslim coastal resorts of Alutgama and Beruwala, where religious riots earlier in the week killed four and wounded 80.

The Muslim Council of Sri Lanka said Islamic clerics instructed mosques to conduct shorter services and asked the faithful to disperse peacefully after lunchtime prayers on Friday.

Muslim-owned businesses shut down in Sri Lanka's capital on Thursday to protest against the riots by extremist Buddhists, defying President Mahinda Rajapakse's plea to stay open. Shops and restaurants in central Colombo were shuttered following the riots at the resorts in which hundreds of homes and businesses were set on fire.

In March last year, two Muslim-owned clothing stores, including No-Limit, came under attack from Buddhist mobs. Muslims account for about 10 per cent of the 20 million population in the mainly Buddhist country.