WASHINGTON - U.S. intelligence and foreign allies have growing evidence that wanted terrorists have been residing in Iran despite repeated American warnings to Tehran not to harbor them.
The evidence, which stretches over several years, includes communications by a fugitive mastermind of the 1996 Khobar Towers bombing and the capture of a Saudi militant who appeared in a video in which Osama bin Laden confirmed he ordered the Sept. 11 attacks, according to U.S. and foreign officials.
They spoke on condition of anonymity because much of the evidence remains classified.
Saudi intelligence officers tracked and apprehended Khaled bin Ouda bin Mohammed al-Harbi last year in eastern Iran, officials said. The arrest came nearly three years after the cleric appeared with bin Laden and discussed details of the Sept. 11 planning during a dinner that was videotaped and aired across the world.
The capture was a coup for Saudi Arabia, which spent months tracking him and setting up the intelligence operation that led to his being taken into custody in exchange for eventual amnesty.
The officials said interrogations of al-Harbi, who is now in Saudi Arabia, have yielded confirmation of many al-Qaida tactics, including how members crossed into Iran after the U.S. began military operations to rout al-Qaida and the Taliban from Afghanistan.
Al-Harbi is believed to have been paralyzed from the waist down while fighting in the 1990s alongside Muslim extremists in Bosnia and Afghanistan, and he surprised intelligence officials when he appeared in the December 2001 video with bin Laden.
"Everybody praises what you did," al-Harbi said on the tape.
U.S. and foreign intelligence agencies also have evidence stretching back to the late 1990s that indicates Ahmad Ibrahim al-Mughassil remains hiding in Iran. He is wanted as one of the masterminds of the Khobar Towers bombing in Saudi Arabia that killed 19 Americans.
Al-Mughassil, who also goes by the alias Abu Omran, has been charged as a fugitive by the United States with conspiracy to commit murder in the attacks and has a $5 million bounty on his head.
U.S. authorities have long alleged the 1996 bombing was carried out by a Saudi wing of the militant group Hezbollah, which receives support from Iran and Syria.
Intelligence agencies gathered evidence, including a specific phone number, as early as 1997 indicating al-Mughassil was living in Iran, and have other information indicating his whereabouts.
U.S. officials have not publicly discussed the Saudi capture of al-Harbi or their evidence on al-Mughassil's whereabouts, but have increasingly raised questions about Iran's efforts to turn over other suspected terrorists believed to be under some form of loose house arrest.
Nicholas Burns, State Department undersecretary for political affairs, told Congress last month that Iran has refused to identify al-Qaida members it has in custody.
"Iran continues to hold senior al-Qaida leaders who are wanted for murdering Americans and others in the 1998 East Africa Embassy bombings and for plotting to kill countless others," Burns said.
Top administration officials have repeatedly warned Iran against harboring or assisting suspected terrorists.
U.S. intelligence this week has been checking some reports, still uncorroborated as of Friday, that Abu Musab al-Zarqawi, al-Qaida's leader of the Iraqi insurgency, may have dipped into Iran, officials said.
On Wednesday, Defense Secretary Donald H. Rumsfeld warned countries in the Middle East not to help al-Zarqawi.
"Were a neighboring country to take him in and provide medical assistance or haven for him, they, obviously, would be associating themselves with a major linkage in the al-Qaida network and a person who has a great deal of blood on his hands," Rumsfeld said.
The U.S. and foreign officials said evidence gathered by intelligence agencies indicates the following figures are somewhere in Iran:
• Saad bin Laden, the son of the al-Qaida leader whom U.S. authorities have aggressively hunted since the Sept. 11 attacks.
• Saif al-Adel, an al-Qaida security chief wanted in connection with the deadly 1998 bombings of U.S. embassies in Africa.
• Suleiman Abu Ghaith, the chief of information for al-Qaida and a frequently quoted spokesman for bin Laden.
U.S. and foreign intelligence officials say they believe those three are under some form of house arrest or surveillance by Iranian authorities.
Kenneth Katzman, a Middle East analyst at the Congressional Research Service, said the conditions that some of suspected terrorists are living under are unclear. Katzman said it's possible they are being held in guarded villas and he doubts any detention is uncomfortable.
"I think that Iran sees these guys as something of an insurance policy," he said. "It's leverage."
Rasool Nafisi, a Middle East analyst who studies conservative groups in Iran and travels there frequently for research, said Iran has returned some lower-rank operatives to their home countries but probably is keeping higher-ranking operatives as a bartering chip.
"Remember, Islamic tradition is very much based on haggling," Nafisi said. "Everything is negotiable, and you haggle for everything. If I were the Iranian government, I'd be very happy to have them and to use them in future negotiations with the United States."