Saudi Arabia said on Tuesday that people it arrested on suspicion of spying this month had direct links to the intelligence services of Iran, its main rival for influence in the Gulf.
A Saudi Interior Ministry spokesman told official media that preliminary investigations - based on physical evidence and statements by the suspects - had found that members of the group had received payment for information.
Riyadh announced a week ago it had arrested 16 Saudis, an Iranian and a Lebanese on spying grounds. The spokesman said the investigation was ongoing.
Members of Saudi Arabia's Shi'ite Muslim minority said the arrested men were from their community and expressed doubt over the veracity of the charges.
Iran said on Sunday it rejected any suggestion it was linked to spying in Saudi Arabia.