The bombers, one of whom was a woman, were all Sri Lankan, officials said. One of them was believed to have studied in Britain and Australia before returning to Sri Lanka, while two others were the sons of a spice tycoon. But the authorities are still investigating whether the Islamic State, which on Tuesday claimed responsibility for the blasts, provided more than symbolic support.

Officials also warned of a continuing terrorist threat and said that other people involved in the attacks remained at large.

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.

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

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.