Officials said that the nine suicide bombers were all Sri Lankans, from mostly educated, middle-class backgrounds, and that other people involved remained at large. The authorities are investigating whether the Islamic State, which on Tuesday claimed responsibility for the blasts, had provided more than symbolic support.

Muslims in some areas of the country are facing a rising backlash.

Sri Lanka’s president asked two top security officials to resign, amid anger that the government had ignored multiple warnings that churches could be attacked.

Go deeper: For older residents of Colombo, Sri Lanka’s capital, the security measures after the bombings are a flashback to the country’s dark days of civil war, and for a younger generation, they are entirely disorienting.

Listen: In the latest episode of “The Daily,” Jeffrey Gettleman, the South Asia bureau chief, discusses the terrorist attack.