The trial--conducted by one judge who investigates the case, prosecutes it, and hands down the verdict and sentence--has been condemned internationally. Both the United States and Israel say the charges are baseless.
The trial began in Shiraz, 885 kilometers (550 miles) south of the capital of Tehran on Thursday, but was adjourned until May 1 to allow lawyers more time to prepare a defense. The verdict could help determine the future of Tehran's relations with the West.
Shortly after the adjournment, provincial judiciary chief Hossein Ali Amiri told relatives of the defendants that four of the accused had confessed, and that judge Sadeq Nourani had ruled the confessions admissible--even though they were not made in the presence of lawyers. He did not say when the confessions were made.
"The four defendants who appeared in court this morning all have confessed to spying for Israel, but have asked the judge for clemency," Amiri said at a news conference.
The 13 suspects were arrested more than a year ago. If convicted, they could receive death sentences. In a similar case three years ago, two Jews were executed.
At the news conference, Haroun Yashayaii, head of Iran's Jewish Society, sat silently among the relatives of the defendants as reporters asked judicial official Amiri about the morning's proceedings.
Yashayaii suddenly got up and yelled out: "This issue has raised tensions among all Jews in Iran." He then broke down in sobs, and many of the defendants relatives began wailing and weeping.
"Your honor, this is an accusation against Iran's whole Jewish community," Yashayaii continued, tears flowing down his face. "We love Iran, and we don't want to flatter anyone when we say we are proud to be living under its flag. We would never do anything against Iran."
Iran maintains religion has no bearing and notes that eight Muslims have been arrested in the case. But Amiri said none of the Muslims were in prison.
Three of the Jewish defendants are on out on bail, and defense lawyer Naseri said he had asked the judge to allow the 10 others to be released for the one-week Jewish Passover holidays that begin Wednesday evening or be allowed to observe the rituals in jail.
The United States has warned that the procedures and outcome of the trial could affect a growing rapprochement between the two countries since President Mohammad Khatami's May 1997 election.
Israel, France, Germany, the United Nations and Amnesty International have either condemned the arrests or called for a fair trial.
Dutch, Swiss and Canadian diplomats were among those at the courthouse.
"Our government is interested in the trial, and we would have liked to see an open trial,'' said Frans J. Potuyt, a Dutch Embassy consular officer. "But we spoke to Iranian authorities this morning and they assured us that the trial would be fair."
Rahmat Farzin, the father of one of the defendants, Ramin, pushed his ailing wife in a wheelchair outside the courthouse. It had taken a 15-hour bus ride to get to Shiraz from Tehran, where they live in poverty, Farzin said.
"Spies are usually well-off. My son has no money at all, so how can he be a spy?" Farzin asked.
Elahe Sharifpour-Hicks, a New York-based researcher for Human Rights Watch, said she had spoken to defense lawyers who told her that they had been given only five days to look at transcripts and meet with the defendants.
At its height, Iran's Jewish community numbered about 100,000 and was still around 80,000 before Iran's 1979 Islamic revolution. Most left after the revolution, and the population has dwindled to about 25,000.
Speaking to reporters after meeting Mubarak, Infrastructures Minister Eli Suissa said the Egyptian leader told him that he had already spoken with Iranian authorities over the case and that he "promised to do his utmost in this respect."
There was no word immediately available from Egyptian officials on whether Egypt, one of Washington's closest Arab allies, was actually intervening on behalf of the 13 Jews.
During the meeting, Suissa handed Mubarak a message from senior Israeli Rabbi Ovadia Yosef in which he pleaded for help in the case.
"I ask and entreat his excellency to intercede with the Iranian authorities on behalf of the Jews who are imprisoned there and are to be tried on very serious charges," said Yosef in the letter.
"I implore his excellency to do everything possible to save them."
Egypt's relations with Iran have considerably improved in the past several years after nearly two decades of animosity over Cairo's granting of asylum to the late Shah of Iran, charges that Tehran supported Muslim militant groups in Egypt and differences over the Middle East peace process.
Egypt has a peace treaty with Israel signed in 1979.