Iran has admitted for the first time it is holding senior members of the al-Qaeda network.
The minister did not name those in custody
Intelligence Minister Ali Yunesi told reporters in the capital, Tehran, that a large number of "small and big" members of al-Qaeda are in Iranian custody.
It is not clear how senior the detainees are, and the minister gave few details.
There has been speculation that al-Qaeda spokesman Sulaiman Abu Ghaith could be one of those detained after Kuwait said earlier this month it had turned down an offer by Iran to repatriate him.
Iran has arrested "a fair number" of the network since the fall of the Taliban and has already expelled some and sent back many others back to their countries of origin, Mr Yunesi said.
Previously, Iran had always refused to reveal any details about members of al-Qaeda it might be holding, saying it was trying to find out their identities.
Last week, Kuwait acknowledged for the first time that Sulaiman Abu Ghaith was in Iranian custody.
Kuwaiti Interior Minister Sheikh Nawaf al-Sabah told Saudi newspaper Okaz that the government had turned down an offer by Iran to extradite Mr Abu Ghaith to Kuwait.
He said his Kuwaiti citizenship had been withdrawn following the 11 September 2001 attacks.
Iran revealed in June it had a number of al-Qaeda suspects in custody and that it had identified some of them.
Reports at the time said the men included al-Qaeda leader Osama Bin Laden's son, Saad Bin Laden, and also his security chief
Saif al-Adel, regarded by some as al-Qaeda's current number three leader.
President Bush accuses Iran and Syria of continuing to harbour terrorists - a charge both countries reject.
Washington believes the suicide attacks in Riyadh in May were planned by al-Qaeda operatives in Iran - a charge that Tehran