DUBAI — An Iranian-American businessman detained in Iran since October has been denied access to his lawyer by authorities, his attorney and family said in an interview and on social media over the last two days.

Siamak Namazi, a dual U.S.-Iranian citizen, was detained by Iran’s Islamic Revolutionary Guard Corps in October while visiting family, according to a source familiar with the matter who declined to be identified. Iranian authorities have not announced any charges against him.

Five other American citizens were released from Iranian prisons more than a month ago as part of an historic prisoner swap with the United States. After their release, U.S. Secretary of State John Kerry said that he had commitments from Iran that Namazi’s case would be resolved soon.

Mahmoud Alizadeh Tabatabaei said in a phone interview Friday that he is representing Namazi and that Iran’s judiciary chief has not yet allowed him to meet with his client. Such permission is required by Iranian law if an individual is accused of national security-related crimes, he said, adding that he has not been officially informed of Namazi’s charges.

“Not me, nor any other lawyer has received such permission from the head of judiciary so far,” Tabatabaei said. “His mother has met him a few times, but his father has not been allowed to see him.”

Tabatabaei said he and Namazi’s mother met this month with a prosecutor who promised to allow more meetings between her and her son.

In a post on Facebook on Saturday, Namazi’s mother, Effie Namazi, said she had not been able to see her son for some time, and did not know his condition. But she said she had received news through his cellmate’s family that Namazi had begun a hunger strike.

“This step by Siamak has greatly increased the worries of his family, because it will certainly hurt his health,” Effie Namazi wrote. “As a mother I ask officials to at least allow for me and his father to meet with Siamak as soon as possible and jointly convince him to quit his hunger strike.”

Tabatabaei identified Namazi’s cellmate as Isa Saharkhiz, a prominent Iranian journalist who also is Tabatabaei’s client.

Hunger strikes have been one way for imprisoned Iranians without other recourse to pressure authorities. Iranian lawyer Nasrin Sotoudeh ended a nearly 50-day hunger strike in 2012 after Iranian officials lifted a travel ban on her daughter.

Namazi was most recently working for Crescent Petroleum, an oil and gas company in the United Arab Emirates. Previously, he headed a consulting firm in Iran. Born in Iran, he was educated in the U.S. and was named a “Young Global Leader” by the World Economic Forum in 2007.

An official at Iran’s Interests Section in Washington, D.C., declined to comment on the case. The U.S. State Department said it could not comment on Namazi’s case because of privacy concerns.

Namazi’s arrest has sent a chilling message to expatriates who hope to participate in Iran’s economic opening following the lifting of nuclear-related sanctions.

Tabatabaei is a prominent lawyer who has represented other detained dual nationals, including former U.S. Marine Amir Hekmati, one of the five Americans released from Iranian prison last month.

Ahmad Kiarostami, a friend of Namazi, said he worried that the hunger strike indicated Namazi had been driven to extreme measures by his detention.

“I don’t know what he wants, I don’t know what he needs,” Kiarostami said in a phone interview. “This is not a solution that the Siamak that I know comes to easily.”