The investigation agency report suggests that the suicide bombings were carried out in Sri Lanka by the ‘well educated youth’.
Nine suicide bombers from mostly educated, middle-class backgrounds carried out the attacks in Sri Lanka that killed more than 350 people on Easter Sunday, the authorities said on Wednesday as they warned of an ongoing terrorist threat and continued making arrests.
The bombers, one of whom was a woman, were all Sri Lankan, officials said. But the authorities were continuing to investigate whether the Islamic State, which on Tuesday claimed responsibility for the coordinated blasts, had provided more than symbolic support, such as by training the attackers or building the bombs.
The authorities said the number of people arrested had risen to 60, and that other individuals involved in the attacks remained at large. As the F.B.I. arrived to assist in the investigation, the American ambassador, Alaina Teplitz, said there were believed to be “ongoing terrorist plots,” and Sri Lanka’s state minister of defense said the danger had not passed.
“There could be still a few people out there,” the minister, Ruwan Wijewardene, said at a news conference. “Right now, we are asking people to be vigilant. Within the next few days, we will have the situation totally under control.”
The Islamic State has not provided any further proof for its claim of responsibility, and Mr. Wijewardene said investigators were trying to determine whether the group had provided training or financing for the attacks. He said they had found no evidence to suggest that the bombers had traveled to the Middle East to fight for ISIS.
The bombings Sunday occurred nearly simultaneously at three churches and three hotels. In the last couple of days, security near the bomb sites has tightened. Schools have been shut until Monday, and the postal department is requiring that items sent by mail be wrapped in front of workers at post offices.