A massive number of documents and other files seized during the 2011 raid that killed al-Qaeda leader Osama bin Laden were released Thursday by the CIA, and appear to bolster U.S. claims that Iran supported the extremist network leading up to the Sept. 11, 2001, attacks.

U.S. intelligence officials and prosecutors have long said Iran formed loose ties to the militant group from 1991 on, something noted in a 19-page al-Qaeda report in Arabic that was included in the CIA's release of 470,000 files, including documents, letters, videos and audio files.

For its part, Iran has long denied any involvement with al-Qaeda. However, the report included in the CIA document dump shows how bin Laden, a Sunni extremist from Iran's archrival Saudi Arabia, could look across the Muslim world's religious divide to partner with the Middle East's Shia power to target his ultimate enemy, the United States.

"Anyone who wants to strike America, Iran is ready to support him and help him with their frank and clear rhetoric," the report reads.

The Associated Press examined a copy of the report released by the Long War Journal, a publication backed by the Washington-based Foundation for Defence of Democracies, a think-tank fiercely critical of Iran and skeptical of its nuclear deal with world powers. The CIA gave the Long War Journal early access to the material.

Hamza bin Laden is seen as an adult at his wedding, in an image from video released by the CIA on Thursday. (CIA/Associated Press)

The material includes a never-before-seen video of bin Laden's son Hamza, who may be groomed to take over al-Qaeda, getting married. It offers the first public look at Hamza bin Laden as an adult. Until now, the public has only seen childhood pictures of him.

The release comes as U.S. President Donald Trump has refused to recertify Iran's nuclear deal with world powers and faces domestic pressure at home over investigations into Russian interference in the 2016 election.

The 19-page report included in the CIA release was available online Wednesday. The CIA later issued a warning about the files on its website, saying that since the material "was seized from a terrorist organization ... there is no absolute guarantee that all malware has been removed." The CIA then took down the files entirely early Thursday, saying they were "temporarily unavailable pending resolution of a technical issue."

"We are working to make the material available again as soon as possible," the CIA said.

The unsigned 19-page report is dated in the Islamic calendar year 1428-2007 — and offers what appears to be a history of al-Qaeda's relationship with Iran. It says Iran offered al-Qaeda fighters "money and arms and everything they need, and offered them training in Hezbollah camps in Lebanon, in return for striking American interests in Saudi Arabia."

Echoes of 9/11 Commission

This coincides with an account offered by the U.S. government's 9/11 Commission, which said Iranian officials met with al-Qaeda leaders in Sudan in either 1991 or early 1992. The commission said al-Qaeda militants later received training in Lebanon from the Shia militant group Hezbollah, which Iran backs to this day.

U.S. prosecutors also said al-Qaeda had the backing of Iran and Hezbollah in their 1998 indictment of bin Laden following the al-Qaeda truck bombings of the U.S. embassies in Kenya and Tanzania that killed 224 people, including 12 Americans.

Al-Qaeda's apparent siding with Iran may seem surprising today, given the enmity Sunni extremists like those of the Islamic State in Iraq and Syria (ISIS) have for Shia.

But bin Laden had run out of options by 1991 — the one-time fighter against the Soviets in Afghanistan had fallen out with Saudi Arabia over his opposition to the ultraconservative kingdom hosting U.S. troops during the Gulf War. Meanwhile, Iran had become increasingly nervous about America's growing military expansion in the Middle East.

"The relationship between al-Qaeda and Iran demonstrated that the Sunni-Shia divisions did not necessarily pose an insurmountable barrier to co-operation in terrorist operations," the 9/11 Commission report would later say.

On Sept. 21, 2008, Iranian Revolutionary Guards members march during a parade ceremony outside Tehran to mark the 28th anniversary of the onset of the Iran-Iraq war. (Vahid Salemi/Associated Press)

Before the Sept. 11 attacks on New York's World Trade Center and the Pentagon in Washington, Iran would allow al-Qaeda militants to pass through its borders without receiving stamps in their passports or with visas gotten ahead of time at its consulate in Karachi, Pakistan, according to the 19-page report. That helped the organization's Saudi members avoid suspicion. They also had contact with Iranian intelligence agents, according to the report.

This also matches with U.S. knowledge. Eight of the 10 so-called "muscle" hijackers on Sept. 11 — those who kept passengers under control on the hijacked flights — passed through Iran before arriving in the United States, according to the 9/11 Commission.

However, the commission "found no evidence that Iran or Hezbollah was aware of the planning for what later became the 9/11 attack."

'A project against Tehran'

For its part, Iran has denied having any relationship with al-Qaeda since the 1998 attacks on the embassies. Iran quietly offered the U.S. assistance after the Sept. 11 attacks, though relations would sour following President George W. Bush naming it to his "axis of evil" in 2002.

On Thursday, Iran's semi-official Fars news agency, which is close to the hardline paramilitary Revolutionary Guard, dismissed the CIA documents as "a project against Tehran."

A man identified by the U.S. Department of Defence as bin Laden watches TV in his compound in Abbottabad, Pakistan, in an undated photo. (Department of Defence/Associated Press)

The 19-page report describes Iranians later putting al-Qaeda leaders and members under house arrest sometime after Sept. 11. It mentions the 2003 U.S.-led invasion of Iraq, saying it put increasing pressure on Iran, especially with the rise of al-Qaeda in Iraq.

"They decided to keep our brothers as a card," the report said.

That would come true in 2015 as Iran reportedly exchanged some al-Qaeda leaders for one of its diplomats held in Yemen by the militant group's local branch. While Yemen described it as a captive exchange, Tehran instead called it a "difficult and complicated" special operation to secure the Iranian diplomat's freedom from the "hands of terrorists."

"The repercussions ... of the Sept. 11 attacks were undoubtedly very large and perhaps above (our) imagination," the al-Qaeda report said.