DUBAI, United Arab Emirates (AP) -- An Iranian-American held in Tehran has reportedly been sentenced to 18 years in prison for "collaboration with a hostile government," yet another dual national convicted in a secret trial since Iran's nuclear deal with world powers.


The sentence handed down to Robin Shahini, a 46-year-old graduate student who lives in San Diego, is the harshest yet for those detained in what analysts believe is hard-liner plan to use them as bargaining chips in future negotiations.


Shahini told Vice News in an interview aired late on Monday that he "just laughed" after hearing his sentence. He acknowledged supporting the protests that followed Iran's disputed 2009 presidential election, but denied being involved in any sort of spying.


"Whatever information they had is all the pictures I posted in Facebook, in my web blog, and they use all those evidence to accuse me," Shahini said in a telephone call from prison.


Iranian judiciary officials could not be immediately reached for comment Tuesday. Iran's mission to the United Nations also did not immediately respond to a request for comment, nor did the U.S. State Department.


Shahini, who traveled to Iran to see his mother who was diagnosed with Alzheimer's disease, was detained on July 11. He left Iran in 1998 and has lived in San Diego for 16 years. He graduated in May from San Diego State University with a degree in International Security and Conflict Resolution and had been accepted to SDSU's graduate program in Homeland Security.


A prisoner exchange in January that freed Washington Post journalist Jason Rezaian and three other Iranian-Americans also saw the U.S. make a $400 million cash delivery to Iran. In September, Iran freed retired Canadian-Iranian university professor Homa Hoodfar amid negotiations to reopen embassies in the two nations.


Last week, Iran's judiciary announced it handed down 10-year prison sentences to Iranian-American businessman Siamak Namazi and his 80-year-old father, Baquer Namazi. Iran earlier sentenced Nazanin Zaghari-Ratcliffe, a British-Iranian woman traveling with her young daughter, to five years in prison on allegations of planning the "soft toppling" of Iran's government.


Still missing is former FBI agent Robert Levinson, who vanished in Iran in 2007 while on an unauthorized CIA mission.


For Shahini, he said he wasn't sure whether he'd file an appeal, but said he also had another option to protest his sentence.


"I do a hunger strike - until either they free me or I die," he said.


By AP