RIYADH — Custodian of the Two Holy Mosques King Salman said on Sunday he was “heartbroken” over a suicide bombing at a mosque in the Eastern Province that killed 21 people, the Saudi Press Agency reported. “Any participant, planner, supporter or sympathizer of this heinous crime will be held accountable, tried and will receive the punishment he deserves,” the King said in a cable addressed to Crown Prince Muhammad Bin Naif, deputy premier and minister of interior. “We were pained by the enormity of the crime of this terrorist aggression which contradicts Islamic and humanitarian values,” the King said. King Salman also ordered to extend urgent treatment to all those injured in the mosque attack, Prince Saud Bin Naif, emir of the Eastern Province, told reporters after visiting the victims at Qatif Central Hospital on Saturday. Prince Saud said King Salman, Crown Prince Muhammad Bin Naif, and Deputy Crown Prince Muhammad Bin Salman, second deputy premier and minister of defense, are closely following the case of the victims. The Interior Ministry identified the bomber as Saudi citizen Saleh Bin Abdul Rahman Al-Qashimi. The militant group had identified him on Friday by a nom de guerre, Abu ‘Ammar Al-Najdi. Al-Qashaami was wanted for being an active member of a Daesh-linked terrorist cell, the ministry said. “The cell was discovered last month, and so far 26 of its members, all Saudi nationals, have been arrested,” the interior ministry said, raising the number of wounded in the mosque attack from 81 to 101. Lab tests showed that the explosive use in the bombing was a military-grade compound known as RDX. The attack in the village of Al-Qudaih in the eastern Qatif region was the deadliest assault by militants in the Kingdom since a 2004 Al-Qaeda attack on foreign worker compounds. The Interior Ministry said the attack against “honorable citizens was carried out by tools controlled by foreign forces that aim to divide the unity of society and pull it into sectarian strife.” But widespread condemnation by Saudi society “sends the message to them that their endeavours have failed,” the ministry said. Grand Mufti Sheikh Abdulaziz Al-Asheikh, called it a “criminal act” which targeted national unity. The United Nations Security Council condemned the mosque attack.