WASHINGTON — A fourth US citizen has been detained in Iran, several sources confirmed to Al-Monitor on Friday, potentially complicating the Biden administration’s pursuit of a prisoner exchange with Tehran.

More than two years after the United States and Iran began indirect talks over a prisoner swap, Tehran was known to be holding three Iranian-Americans — Siamak Namazi, Emad Shargi and Morad Tahbaz — on charges US officials say are baseless.

On Friday, five sources with knowledge of the situation told Al-Monitor that the United States was seeking the release of a fourth individual detained by Tehran. Multiple sources said the detainee is a male dual US-Iranian national, with one source saying he was arrested in late 2022.

Experts speculated that actors within Iran’s system had tried to sabotage the prisoner talks by arresting an additional American. It’s also possible that Iran’s negotiators sought another US citizen to restore balance to the negotiations after releasing a fourth American, Baquer Namazi, on humanitarian grounds in October 2022.

In late June, Middle East Eye reported that US officials had added a fourth name to the list of Americans they were seeking from Iran. Semafor also reported on the detention of a fourth American. 

Asked to confirm the reports, a spokesperson for the National Security Council referred Al-Monitor to national security adviser Jake Sullivan’s interview with CBS’s "Face the Nation" on Sunday.

"We have tried very hard to secure the release of the four unjustly detained Americans in Iran; we have done so since the day that President Biden took office,” Sullivan said. 

Last month, Washington and Tehran appeared to be on the verge of an agreement that would bring home the American prisoners in exchange for Iran gaining limited access to billions of dollars in assets frozen abroad. Omani Foreign Minister Sayyid Badr Albusaidi, whose country has helped facilitate the prisoner talks, told Al-Monitor in a June 14 interview that the two sides were close to a deal. Albusaidi met with his Iranian counterpart, Hussein Amir-Abdollahian, in Tehran earlier this week. 

The Biden administration has previously said it would not accept a “partial deal” with Iran that leaves Americans behind, as occurred in 2016. Siamak Namazi, a businessman detained in 2015, was the only American not returned home as part of a prisoner exchange that occurred the same day the Iranian nuclear deal took effect. Namazi, now the longest-held American prisoner in Iran, was also left out of two subsequent prisoner releases under the Trump administration.

A State Department spokesperson urged Iran to release all wrongfully detained Americans “without delay,” describing their imprisonment as “outrageous.”

“We will not discuss the details of any efforts to secure the release of US citizens wrongfully detained by Iran, including any numbers of US citizens currently in Iran,” the spokesperson told Al-Monitor Friday. “Such discussions would be sensitive and highly consequential to those individuals and their families.”

A spokesperson for the Iranian Mission to the United Nations declined to comment on the number of detained Americans but said negotiations were "ongoing."

The jailing of foreigners and dual citizens is widely seen as a way for Iran to gain leverage in negotiations for frozen assets, sanctions relief and other concessions. In late May, Belgium and Iran exchanged prisoners in an Omani-mediated deal. A week later, Tehran released three detainees from Denmark and Austria.

In addition to the four detained Americans, Iran is also holding Shahab Dalili, a legal permanent US resident. His family has urged the Biden administration to include him in any exchange.