IRVINE (AP) Friends and colleagues of a dual Iranian and American citizen worry that he has been taken into custody in Iran following a trip there to visit his ailing mother.

Ali Shakeri, 59, was supposed to leave Iran and fly to Europe on May 13, but never arrived at his destination. His ticket has been canceled and his luggage was taken from the airline's possession, according to the group Human Rights Watch, a non-governmental organization.

Shakeri made one call to family members and said there was a "misunderstanding" but that he would be OK, said Hadi Ghaemi, an Iran analyst for the group. It appears no one has heard from him since. The group now believes the Iranian government probably detained Shakeri at a Tehran airport and might be interrogating him in an isolated location.

Shakeri is a founding board member at the UC Irvine's Center for Citizen Peacebuilding.

Iranian officials have not commented publicly on Shakeri's whereabouts. In recent weeks, two Iranian American scholars with dual citizenship have been imprisoned while visiting the country. The detention of one of those scholars, Haleh Esfandiari, bears close parallels to Shakeri's disappearance.

Esfandiari, a researcher based at the Woodrow Wilson International Center for Scholars in Washington, traveled to Iran late last year to visit her 93-year-old mother. When she headed to the airport to leave Iran on Dec. 30, she was stopped by knife-wielding men in masks, according to center officials.

She was interrogated extensively and, earlier this month, imprisoned. The Iranian government this week announced she was being charged with setting up a network to overthrow the Islamic establishment. Her husband, Shaul Bakhash, denied the allegations as "totally without foundation."

Javad Payam, a friend of Shakeri's who edits a Persian magazine in Laguna Hills, is anxious. He has interviewed former detainees who have described being locked in cells without windows and forced to sleep on the floor.

"When you look at the history of the regime for the past 25 years, whoever has a voice lands in jail, is killed or disappears. It's nothing new," said Payam, who met Shakeri at a rally in Los Angeles. "We pray and hope nothing happens to him."