DUBAI, United Arab Emirates -- Two Iranian-Americans serving 10-year prison sentences on spying charges in Iran should be immediately freed and paid restitution, a United Nations panel said on Monday, calling their "arbitrary" detention part of an "emerging pattern" by Tehran of targeting dual nationals.

The decision by a group of U.N. experts on the case of Siamak and Baquer Namazi comes as Iranian President Hassan Rouhani attends the world body's annual meeting in New York.

It puts new pressure on the moderate cleric's government to confront hard-liners within Iran's paramilitary Revolutionary Guard and judiciary, which repeatedly has arrested and prosecuted those with Western ties in the wake of the country's 2015 nuclear deal.

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However, it remains unclear whether Rouhani has the power within Iran's clerically overseen government to free those detained, as analysts and family members of those held believe they will be used as bargaining chips in future negotiations.

Siamak Namazi, a 46-year-old businessman who promoted closer ties between Iran and the West, was arrested in October 2015. His 81-year-old father Baquer, a former UNICEF representative who served as governor of Iran's oil-rich Khuzestan province under the U.S.-backed shah, was arrested in February 2016, apparently drawn to Iran over fears about his incarcerated son.

Earlier this summer, CBS News' Margaret Brennan spoke to Siamak Namazi's brother, Babak, who is pleading for the release of his family members.

"Everything I hear terrifies me, and it terrifies me more and more every day," he said. "All I ask for obviously is for their safe return and for their immediate return before it's too late."

Iran does not recognize dual nationalities, meaning those detained cannot receive consular assistance. The two Namazis, like other dual nationals, faced secret charges in closed-door hearings in Iran's Revolutionary Court, which handles cases involving alleged attempts to overthrow the government.

In August, their Washington-based lawyer Jared Genser said that they lost an appeal of their convictions for "collaboration with a hostile government," namely the United States. Iranian authorities later acknowledged they lost their appeal.

In their report, the U.N.'s Working Group on Arbitrary Detention dismissed the cases against the two men, saying their case is part of "an emerging pattern involving the arbitrary deprivation of liberty of dual nationals."

"There is no evidence either Mr. S. Namazi or Mr. B. Namazi had a criminal record, including in relation to national security offenses," their report read. "There is nothing to indicate that they have ever acted against the national interests of the Islamic Republic of Iran."

The experts' report said Iran's government did not respond to its queries about the Namazis' case. Iran's office at the U.N. did not immediately respond to a request for comment Monday from The Associated Press.

"This decision explains in detail precisely why the detention of the Namazis is illegal and in violation of international law," Genser said in a statement. "It is time for Iran to resolve these cases and allow the Namazis to be reunited with their family."

Others with ties to the West detained in Iran include Chinese-American graduate student Xiyue Wang, who was sentenced to 10 years in prison in Iran for allegedly "infiltrating" the country while doing doctoral research on Iran's Qajar dynasty. Nazanin Zaghari-Ratcliffe, a British-Iranian woman, was sentenced to five years in prison on allegations of planning the "soft toppling" of Iran's government while traveling with her young daughter.

Iranian-American Robin Shahini was released on bail last year after staging a weekslong hunger strike while serving an 18-year prison sentence for "collaboration with a hostile government." Shahini is believed to still be in Iran.

Also in an Iranian prison is Nizar Zakka, a U.S. permanent resident from Lebanon who advocates for internet freedom and has done work for the U.S. government. He was sentenced to 10 years last year on espionage-related charges.

Former FBI agent Robert Levinson, who vanished in Iran in 2007 while on an unauthorized CIA mission, remains missing as well.