Sri Lankan prosecutors Monday indicted the alleged mastermind of the 2019 Easter Sunday suicide bombings along with 24 men they say were co-conspirators in the island's worst single terror attack, AFP reported.

Almost three hundred people including dozens of foreign nationals were killed in the April 21 attacks on three churches and three luxury hotels, in a wave of killings targeting Sri Lanka's Christian community.

Prosecutors have brought over 20,000 charges against the suspects, three of whom have already been accused of terrorism by the US Justice Department.

Prosecutors told the court that US and Australian forensic experts assisted investigators in tracking down the backers of the eight-member suicide squad responsible for the attacks.

Sri Lanka authorities have accused their ringleader, Mohamed Naufar, of being the mastermind of the deadly suicide bombings and of being a member of the ISIS group.

Former police chief Pujith Jayasundara and top defense official Hemasiri Fernando are also being prosecuted separately for failing to act on repeated intelligence warnings of a possible ISIS attack.