Iran's foreign ministry on Monday summoned the Saudi ambassador to protest over Riyadh's treatment of Iranian nationals jailed in the kingdom, the official IRNA news agency reported.
Ministry officials questioned the ambassador over "worrisome" reports on the treatment of Iranian nationals jailed in the city of Dammam, capital of the Eastern Province that is home to most of the kingdom's Shiite minority.
"Failure to answer (to Iran's concerns) does not relieve (the kingdom) of its legal and international obligations under relevant conventions on prisoner rights," IRNA quoted an unnamed ministry source as saying.
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The report did not specify the number of Iranians held in Saudi prisons.
Relations between Tehran and Riyadh have been strained since a US allegation last year of an Iranian plot to assassinate the Saudi ambassador to Washington, something Tehran has repeatedly denied.
Another point of contention has been the Saudi military intervention in March 2011 in the Sunni-ruled Gulf kingdom of Bahrain to help its government quash pro-democracy protests led by the state's Shiite majority.
The summoning of the Saudi ambassador came on the eve of a meeting of foreign ministers of the six Gulf Cooperation Council states in Doha to discuss a simmering islands dispute between Iran and the United Arab Emirates.