Saudi Arabian officials have arrested 10 more members of an alleged Iranian-linked spy ring, according to the interior ministry, following the detention of 18 other such ”spies” in March.

In the new batch of arrestees, eight are Saudis, and the other two originated in Turkey and Lebanon.

Most of the 18 arrested in March were also Saudi nationals, plus one Iranian and one Lebanese. (The Lebanese suspect has since been released).

Iran has denied it has engaged in any intelligence operations in the Saudi kingdom.

Iran and Saudi Arabia, two of the most powerful nations and oil exporters in the Middle East, have long been in conflict, partly due to religious issues -- the Saudis are predominantly Sunni Muslims, while Iran is a Shia Muslim theocracy.

Reuters reported that all the Saudis under detention since March are members of the kingdom’s Shia minority, who predominate in the country’s oil-rich eastern regions.

Relations between Teheran and Riyadh – never warm in the first place – worsened after the Saudis sent troops into Bahrain to quell a rebellion by that country’s Shia majority against its Sunni rulers in spring 2011.

Since then, Shias in eastern Saudi Arabia have periodically protested and engaged in clashes with security forces and police.