Two new confessions were reportedly made in court when the trial resumed in Shiraz on Monday, a defense lawyer said.
Farhad Seleh, 40, a textile shopkeeper and religion teacher, and Asher Zadmehr, 54, a university language professor, pleaded guilty to espionage, said Esmail Naseri, a spokesman for the defense team.
Their confessions raised to eight the number of defendants who have pleaded guilty. So far only one defendant, Farzad Kashi, has denied the charges.
Seleh and Zadmehr were the only ones in the dock Monday. A third defendant, Javid Bent-Yacoub, 42, a shopkeeper, was brought to the courthouse, but judiciary officials said it was uncertain whether he would be heard Monday.
The defendants' relatives stood outside the courthouse, some looking distraught. They refused to talk to the press.
Before the hearing began, Naseri told The Associated Press that if the court were to allow more confessions to be broadcast without authorization, ``we will file a lawsuit against all those involved.''
Iranian state television has broadcast confessions of two defendants - Dani Tefilin, a shoe salesman, and Shahrokh Paknahad, a religion teacher - in which they said separately they were trained and paid by Israel to gather secrets in Iran.
``The interviews have been shown without our permission and without our clients consulting us about giving them,'' Naseri said.
Naseri said lawyers would seek permission to interrogate any witnesses who might have accused their clients of espionage, and called on the court to produce more evidence.
The lawyers maintain that confessions alone are not enough and that the court must show that secret information was handed to Israel, which Iran considers its arch foe. Iranian citizens, Jews included, are prohibited from having any contact with Israel or Israelis.
Israel has denied that any of the defendants were its spies and claims the 13 have been charged simply because they are Jews. Some of the defendants are known to have relatives in Israel.
Defense lawyers and rights groups in the West have questioned the fairness of the closed-door revolutionary court, where the judge is also the prosecutor and jury. Questions have also been raised over whether the confessions have been made under duress.
Two lawyers from the French-based organization Lawyers Without Borders, Pierre Dunac and Stephanne Zerbib, came to the courthouse Monday and offered assistance to the defense team. Judiciary officials said they could not attend the hearings.
The trial has had a negative impact on the 25,000 Jews in Iran - the largest Jewish community in the Middle East outside Israel. Several Jews have told reporters that the case has isolated them from their Iranian compatriots.
Iranian Jews have faced some government restrictions since the 1979 Islamic revolution, but they have been free to practice their religion and generally face little overt discrimination.