A Roman Catholic church in this town west of the capital Colombo was attacked by unidentified arsonists who destroyed furniture and religious statues, police said.
The men set fire to everything inside the St Michael's church in the pre-dawn attack, police said, even though the it was close to the local police station.
"An unarmed watcher had been chased away by the attackers who set fire to everything that was inside the single-storey building," a police officer at the scene told reporters.
He was unable to say how the attackers carried out the arson unnoticed by the police station located just 200 yards away. A forensic investigation was underway.
The area surrounding the church at Katuwana, Homagama, about 40 kilometers (25 miles) west of Colombo, was cordoned off by armed police who did not allow press photographers to get into the premises before forensic experts could complete their work.
Catholic priest Chaminda Wanigasena said there was no resident clergy at the church, which was managed by a larger church in the neighborhood.
He said the church had been attacked by arsonists earlier this year prompting authorities to deploy police guards outside, but the armed protection had been withdrawn recently.
No one claimed responsibility or was arrested for the earlier attack.
"We believe the same group that attacked the church earlier was responsible for today's attack as well," the priest said. "All the statues and furniture inside the church have been destroyed."
Attacks against churches escalated earlier this year following the death of a controversial Buddhist monk, Gangodawila Soma, who led a campaign against religious conversions.
Christians make up 7.5 percent of the population of Sri Lanka, where more than 60,000 people have died in a 30-year armed campaign by separatist Tamils, who are predominantly Hindu.
Sri Lanka's constitution grants the foremost place to Buddhism, which is practiced by nearly 70 percent of the island's 18.66 million people. Hindus make up about 15 percent and Muslims about 7.5 percent.