Wednesday's release followed announcements earlier this week that a trial is imminent for all 13 of the imprisoned Jews.
"Obviously we're glad about this development, but we can't forget there are 13 people, and we won't start celebrating until all 13 are released," said Sam Kermanian, secretary-general of the Los Angeles-based Iranian American Jewish Federation.
The three released are 16-year-old Navid Balazadeh, the youngest of the defendants, his uncle Nejad Bouroghi, who is a religious leader in the city of Isfahan, and Omid Tepilin of Shiraz, said Kermanian.
The 13 Jews -- religious and community leaders -- have been held in a jail in the southern Iranian city of Shiraz since the spring. They have been accused of spying for Israel and the United States but have not been formally charged. Both Israel and the United States have vehemently denied the accusations against them.
They face the death penalty if convicted.
The three released this week will still face a trial should the government bring formal charges against them, Kermanian said, "but I'm hoping this indicates that their files, like the others', don't include sufficient evidence to bring charges, and that's why they decided to release them."
Malcolm Hoenlein, the executive vice chairman of the Conference of Presidents of Major American Jewish Organizations, said of the release: "If this is a positive message, we receive it as such, but it's a very limited one."
Advocates for the prisoners still worry that the accused will not receive a fair trial.
They also believe a trial is not likely to occur until after Iran's upcoming elections.
Many observers believe that the arrests and accusations are part of a power struggle between conservative hard-liners and President Mohammad Khatami, who has made overtures to the West.
The Feb. 18 elections are being seen as a contest between the two forces vying for power.
Iranian officials have not detailed the evidence against the suspects, but hard-line elements of the judiciary reportedly have said documentation of the alleged crimes proves their guilt.
The case sparked an international outcry, and those working on behalf of the detained have alternated between public and private diplomacy to press their cause.
In recent months, American Jewish advocates -- while hoping for the prisoners' release -- have also been working to try to ensure that the prisoners receive a fair trial.
"Our preference is they should be released now," Hoenlein said. "They've suffered enough no matter what they've done, and none are guilty of espionage."
A trial might be better than endless delays, said Hoenlein, but "has to be public with representation and outside participation as has been promised all along."
Kermanian, agreed, saying a trial presents an opportunity for Iran to "show to the world that it's serious about its declarations regarding the rule of law, its civil rights, or depending on the outcome, to essentially prove they are not serious.''
He expressed concern about the judicial process, especially that the Jews be given lawyers and that the lawyers be given adequate time to review the charges and prepare a defense.