Sri Lankan police raided the headquarters of a hard-line Islamist group founded by the suspected ringleader behind the Easter suicide bombings of churches and hotels, a Reuters witness said, as Sunday mass was canceled due to fears of further attacks.

Armed police in the town of Kattankudy searched the headquarters of the National Thawheedh Jamaath (NTJ) and detained one man at the premises, a Reuters reporter at the scene said. Police did not comment.

On Saturday the government banned the NTJ under new emergency laws. The authorities believe Zahran Hashim, the founder of NTJ, masterminded and was one of the nine suicide bombers in the attacks on Easter Sunday that killed 253 people. Islamic State claimed responsibility for the attacks.