Saudi Arabia today said it foiled an Islamic State plot to bomb its Defence Ministry headquarters and arrested several people suspected of carrying out espionage in the kingdom on behalf of foreign powers. The announcements were made by a security official to state news agency SPA and a security source to Reuters. <br/><br/>An official from the Presidency of State Security said, the suspected bombers were identified as two Yemeni nationals living under aliases in the kingdom. He said they were detained along with two Saudi citizens, suspected of involvement in the attack planned for the capital Riyadh. Saudi authorities said they seized grenades and firearms during the operation to foil the attack.<br/><br/>In a separate news item, SPA quoted a security source saying authorities uncovered intelligence activities for the benefit of foreign parties by a group of people it did not name. A Saudi security source, told Reuters that the suspects were accused of espionage activities and having contacts with external entities including the Muslim Brotherhood, which Riyadh has classified as a terrorist organisation.