WASHINGTON - President George W Bush said on Monday the United States was trying to determine whether Iran was involved in the September 11 plot and accused the government of harbouring al Qaeda leaders.
"We want to know all of the facts," Bush said when asked about reports that at least eight of the 19 hijackers passed through Iran before attacking the United States.
The commission investigating the attacks will detail these and other al Qaeda links to Iran in its final report this week, raising new questions about why Bush turned his focus to Iraq soon after September 11, 2001.
The commission has found more al Qaeda contacts with Iran than with Iraq, officials said.
White House spokesman Scott McClellan said there was "no evidence that there was any official involvement between Iran and the September 11 attacks".
The US intelligence community has been harshly criticised for overstating the Iraqi threat before the war, leading to calls for its overhaul and for the creation of a Cabinet-level intelligence czar.
McClellan said Bush was willing to consider this step, although acting CIA director John McLaughlin on Sunday questioned whether it was necessary.
Bush noted McLaughlin had said "there was no direct connection between Iran and the attacks of September 11".
But Bush said the case was not closed. "We will continue to look and see if the Iranians were involved... As to direct connections with September 11, we're digging into the facts to determine if there was one," he said.
Bush said Iran, which he branded part of an "axis of evil" along with Iraq and North Korea, was "harbouring al Qaeda leadership." He urged Tehran to have them "turned over to their respective countries" of origin.
"If the Iranians would like to have better relations with the United States there are some things they must do," including halting the country's alleged nuclear weapons programme and support for terrorism, Bush said.
Former CIA director Robert Gates, who co-authored a Council on Foreign Relations report on Iran, said al Qaeda "probably has either, if not used Iran as base, then used it for safe passage and various other things".
Former national security adviser Zbigniew Brzezinski, who worked with Gates, said reports of the passage through Iran of al Qaeda operatives prior to September 11, 2001 is "not direct evidence that they are complicit in 9/11".
The New York Times newspaper reported on Sunday that the Iranian government had ordered its border guards not to stamp the passports of Saudi al Qaeda members moving through Iran after training in Afghanistan.
An Iranian stamp could have made the al Qaeda members subject to additional scrutiny upon entering the United States, US officials said.
Iran acknowledged some of the September 11 attackers may have passed through illegally, but said it had since tightened border controls. It said any attempts to tie the country to al Qaeda, the militant network which carried out the attacks, were part of US election-year "news propaganda".