A man claiming to be a former member of the Jehovah's Witnesses was detained for questioning about his alleged involvement in setting off homemade bombs at a meeting of the group in the southern Indian state of Kerala on Sunday, killing two women and injuring dozens of other people, police said.
A second woman had died, chief minister Pinarayi Vijayan told reporters at a briefing, adding that 17 people were in intensive care with five in a critical condition.
Health minister Veena George earlier told Reuters a 12-year girl with 95% burns was also in a critical state.
Dominic Martin posted a video on Facebook claiming responsibility for the attacks, before surrendering shortly after noon at a police station in Thrissur district, about 40 km (25 miles) from the site of the explosions.
"Dominic is still being questioned in Kochi. He is in our custody but we have not recorded his arrest so far," police public relations officer Pramod Kumar told Reuters.
"We are still trying to ascertain the veracity of his statement, it will take some time. We are not in a position to confirm his involvement in the case right now, investigation is ongoing," he added.
The incident took place during a Jehovah's Witnesses convention in Kalamassery, about 10 km (6 miles) northeast of Kochi city.
TA Sreekumar, regional spokesperson for the Jehovah's Witnesses, told Reuters that Martin was not a registered member of the group. He said about 2,300 people attended the three-day event but he was unaware if Martin was present.
Sreekumar confirmed to Reuters that there were at least two big explosions at the centre.
"I am taking full responsibility for this. I carried out the bomb explosion. I am making this video to make it clear why I did this," Martin said in a near-six-minute Facebook video which was online for about 4 hours before it disappeared.
Martin said about he believed the Jehovah's Witnesses' teachings were "antinational" about six years ago and that he had tried to talk to the group about changing their views.
Preliminary investigation showed that an improvised explosive device was used, Kerala Director General of Police Shaik Darvesh Saheb told reporters earlier.
Chief Minister Vijayan said police were taking the incident seriously, a special team of 20 members was investigating, and he would have more clarity at an all-party meeting on Monday morning.
"The explosions occurred seconds after the end of a prayer as part of the day's event. The first blast took place in the middle of the hall. Seconds later, two more explosions rocked simultaneously on either sides of the hall," Sreekumar had earlier told mathrubhumi.com, a local media outlet.
Jehovah's Witnesses are an international Christian denomination founded in the United States around 1870. They are best known in many countries for door-to-door evangelism.
The group said it has about 60,000 followers in India.