Saudi Arabia has said that several people it arrested on suspicion of spying this month had direct links to the intelligence services of Iran.
A security spokesman for the interior ministry said on Tuesday that Iranian intelligence had paid the suspects "in exchange for information and documents about important sites".
"Preliminary investigations, physical evidence which has been collected, and statements from the accused in this case, have shown a direct link between members of this cell and Iran's intelligence apparatus," the spokesman was quoted by the kingdom's official news agency as saying. He said the investigation was ongoing.
Riyadh announced a week ago it had arrested 18 suspects, including 16 Saudis, an Iranian and a Lebanese, on suspicion of spying.
Tehran denied on Sunday that it was linked to the alleged spying in Saudi Arabia.
Members of Saudi Arabia's Shia Muslim minority said the arrested men were from their community and expressed doubt over the veracity of the spying charges.
The 16 Saudis arrested included a paediatric doctor, a university professor and a banker, as well as two well-known clerics.
'Escalate sectarian tension'
Relatives and friends of some of those arrested said they did not believe the men had strong political views.
In a statement issued by 37 Saudi Shia leaders last week, including religious leader Ayatollah Hassan al-Saffar, they accused the government of using the spying charges to escalate sectarian tension to detract public attention from other issues.
The allegation marks an escalation in friction between the two major oil producers, which face each other across the Gulf.
Sunni Muslim Saudi Arabia and Iran, with a predominantly Shia population, have backed opposing sides in armed conflicts and political struggles across the Middle East, particularly in Syria and in Bahrain.
Riyadh has also accused an unnamed foreign power, which officials have privately named as Iran, of stirring unrest among its own Shia minority in the country’s northeast, something Tehran has denied.
Saudi Arabia also pointed to an alleged Iranian plot, announced by US police in 2011, to assassinate the kingdom's ambassador in Washington. Iran denies involvement in the plot.
Tehran said last week that a drunk Saudi diplomat had killed an Iranian national in a car accident.