Scholar Haleh Esfandiari -- who was in isolation at Evin prison for some three months -- was able to leave the country on September 3. Authorities have also returned the passport of Radio Farda broadcaster Parnaz Azima, who had been prevented from leaving Iran for several months.
Iranian officials have said they plan to release another detained Iranian-American scholar, Kian Tajbakhsh, on bail.
The decision-making process within the Iranian government can be obscure, and officials do not officially inform the public of the reasons behind their decisions.
The arrest of the four Iranian-Americans, their detention, and the two recent releases provide an example of the murkiness of Iranian politics.
Authorities have not said what prompted the sudden release of Esfandiari, the director of the Middle East Program of the Woodrow Wilson Institute. Esfandiari was charged with serious security crimes, including involvement in what authorities have described as a U.S. plot aimed at destabilizing the Iranian regime.
Officials have only said that the investigation into her case was completed and suggested she would have to return to Iran for the trial.
Azima has also been told that her case remains open and that there will be a court session at an unspecified date.
But there are doubts as to whether there will be an actual trial in their cases or in those of the other Iranian-Americans who have been charged by Tehran.
Bill Samii, an Iran analyst at the Center for Naval Analyses and former RFE/RL regional analyst, believes that the Iranian government realized it got "maximum value" out of the detentions and came to the conclusion that there is no benefit in keeping them.
"The message has been sent to other Iranians that if you cooperate with the U.S. in any kind of activity that could be labeled as antiregime then you face imprisonment at the very least," Samii says. "So they sent a message with Tajbakhsh, with Esfandiari, with Azima, and now the government has realized that if [it] actually has open trials it will look pretty ridiculous for the regime so they just release these individuals, send them home and you can be pretty certain that these people after they've been imprisoned in Iran, if they leave the country, I think they'd be pretty reluctant to go back to Iran."
Esfandiari was released on a bail of about $300,000. Authorities have told Azima that her mother's house -- which was put up as bail for her -- would not be returned. She is facing charges of spreading propaganda against the government.
Samii says Tehran uses the heavy bails as a pressure tool.
"Most of them when they pay these very high bails to get out of jail, they have to mortgage family members' homes, so that's always something that the Iranian government can hold over their heads, basically threatening that if you come back we will arrest you again and you'll lose the bail," Samii says. "Your family member, your mother, or whoever, will lose his or her home."
Analysts believe the arrest of Iranian-Americans is part of a broader crackdown on students, rights activists, and all dissenting voices. The crackdown comes at a time when Tehran is under increasing U.S. pressure over its nuclear program and its role in Iraq and Afghanistan.
'Sending A Message'
Faraj Sarkuhi, an exiled Iranian journalist, believes that by making the arrests Iran is sending a strong message to its critics.
"One of its goals is to send a message and tell critics to remain silent, if not they could meet the same fate as those who have been arrested," Sarkuhi says. "But this message is usually not effective because at least in the past 20 years we've seen that there have been many arrests, many forced [confessions], but despite that Iranian freedom fighters have continued their work inside Iran."
Sarkuhi credits human-rights groups, academics, and others for the release of the Iranian-Americans and also extensive media coverage that brought attention to their plight.
"[They] use all possible methods in their factional disputes or fight against those who oppose them without considering its results," Sarkuhi says. "In [the case of Iranian-Americans] nothing new was added to the case of the Islamic republic. Even without the arrest of Haleh Esfandiari and the others the Islamic Republic of Iran was known as being an establishment that violates human rights, arrest critics and opposition members, and executes people."
Some observers have said that by agreeing to allow citizens with dual citizenship to leave the country, Tehran was signaling a willingness not to worsen relations with Washington further.
Analyst Samii, however, says it is unclear why Tehran would make such a move now.
"As I speculate, I wonder if the tensions of the Iranian-Americans are somehow connected with the detentions of Iranian military personnel in Iraq," Samii says. "So perhaps there are some sort of negotiations taking place or even if it's not negotiations, a hope on the Iranian side that if we release these people maybe the Americans will release our soldiers who are being held in Iraq."
The United States has welcomed Iran's decision to permit Esfandiari and Azima to leave the country. U.S. State Department Deputy Spokesman Tom Casey said on September 5 that Iran should also release the other Iranian-Americans who are jailed in Iran.
They include Tajbakhsh, a consultant with the Open Society Institute, and peace activist Ali Shakeri.
INSIDE THE ISLAMIC REPUBLIC: Iran is a theocratic Islamic republic governed under a 1979 constitution that was revised in 1989, when presidential powers were expanded and the prime minister's post was abolished.
Appointed -- not elected -- offices and bodies hold the real power in the government. The supreme leader, who serves as a chief of state would, is appointed for life by an Islamic religious advisory board that is called the Assembly of Experts. The supreme leader oversees the military as well as the judiciary and appoints members of the Guardians Council and the Expediency Council.
The Guardians Council -- some of whose members are appointed by the judiciary and approved by the parliament -- works closely with the government and must approve political candidates and legislation passed by the parliament. The Expediency Council is responsible for resolving legislative disputes that may arise between parliament and the Guardians Council over legislation.
The president, who is popularly elected for a four-year term, serves as the head of government. The legislative branch is made up of a 290-seat body called the Majlis, whose members are elected by popular vote for four-year terms...(more)
RFE/RL's coverage of Iran