The US Justice Department charged three Sri Lankans on Friday with supporting terrorism for their participation in the 2019 Islamic State Easter attack that killed 268 people.

The department said the three were part of the "ISIS in Sri Lanka" group behind the attacks on three churches and three luxury hotels in three cities on the Christian holiday on April 21, 2019.

The Islamic State claimed responsibility and called the well-planned attacks a retaliation for Western coalition actions against the group in Syria.

Five Americans were among the dead.

The three charged are Mohamed Naufar, the "second emir" and a recruiter and trainer for ISIS in Sri Lanka; Mohamed Anwar Mohamed Riskan, who allegedly helped manufacture the bombs used in the attacks; and Ahamed Milhan Hayathu Mohamed, who killed a police officer in the attack, the Justice Department said.

All three are in custody in Sri Lanka, and the Justice Department said it will support their prosecution in that country while maintaining the US charges in the event they gain their freedom.

"This case clearly demonstrates that the United States will take decisive action to ensure terrorists face justice when they target Americans anywhere in the world," said Nick Hanna, the US federal prosecutor in Los Angeles, where the case was filed.

"The United States remains confident in the Sri Lankan authorities' ability to bring the perpetrators to justice -- and this complaint makes clear that we stand ready with these charges in the event the defendants attempt to evade justice," he said in a statement.

The three were charged with providing material support to a designated foreign terrorist organization, and Naufar and Milhan were charged with helping in military-type training for the Islamic State.