An Iranian American imprisoned in Iran for more than seven years appealed to US President Joe Biden on Monday to bring him home and said he was starting a seven-day hunger strike.

Siamak Namazi made the plea in a letter to Biden seven years to the day that Iran released five other US citizens in a prisoner exchange choreographed to coincide with the implementation of the 2015 Iran nuclear deal.

"When the Obama Administration unconscionably left me in peril and freed the other American citizens Iran held hostage on January 16, 2016, the US Government promised my family to have me safely home within weeks," Namazi, 51, said in the letter to Biden released by his lawyer, Jared Genser.

"Yet seven years and two presidents later, I remain caged in Tehran's notorious Evin prison," he added.

Namazi asked Biden to spend one minute a day for the next week thinking about the suffering of US citizens detained in Iran, who include environmentalist Morad Tahbaz, 67, who also has British nationality, and businessman Emad Shargi, 58.

Namazi and others have been detained on trumped-up charges in what seems to be Iran's long history of arresting foreigners as hostages.

Namazi, whose father was allowed to leave Iran in October for medical treatment after being detained on espionage-related charges rejected by Washington, said he would be on a hunger strike for the same seven days.

Asked for comment, a White House national security council spokesperson told Reuters the government was committed to securing Namazi's freedom.