The United States probed links between the government of Saudi Arabia and the 9/11 attacks, finding multiple suspicions but no proven ties, documents declassified Friday showed.

Part of a Congressional report that had been kept under wraps for more than a decade showed US intelligence believed that Saudi officials may have had multiple contacts with some of the 9/11 hijackers.

Fifteen of the 19 hijackers were Saudi citizens.

The findings however show no smoking gun for Saudi involvement, but rather an inability to "identify definitively" Saudi links to attacks on US soil and global terror.

"While in the United States, some of the 9/11 hijackers were in contact with, and received support or assistance from, individuals who may be connected to the Saudi government," the declassified document said.

One individual on the US East Coast, believed to be from the Saudi interior ministry, raised suspicions when appearing to fake a seizure during FBI questioning about his links to a hijacker.

He was later released from hospital and managed to flee the country before he could be questioned again.

Intelligence also turned up suggestions that Osama bin Laden's half-brother worked at the Saudi embassy in Washington and was associated with a friend to Egyptian hijack leader Mohammed Atta.

In California, a suspected Saudi intelligence operative was believed to have provided "substantial assistance" to two other hijackers.

The phone book of an Al-Qaeda operative captured in Pakistan meanwhile pointed to US contacts, notably a company which managed a Colorado property of the then Saudi ambassador.

- 'Unacceptable' intel gaps -

The year-long Congressional investigation also expressed anger about gaps in US intelligence about Saudi Arabia's possible links to terror, deeming them "unacceptable" given the "magnitude and immediacy of the potential risk to US national security."

Former president George W. Bush had ordered that part of the report be classified.

Bush's administration had cited the need to protect the methods and identities of US intelligence sources.

But there was also concern that the report could damage relations with an important Middle Eastern ally and oil exporter.

President Barack Obama had decided to declassify the so-called "28 pages."

The revelations are likely to prompt a fresh round of handwringing about Washington's close ties with Riyadh and Saudi Arabia's role in fostering violent extremism.

Saudi Ambassador to the United States Abdullah Al-Saud welcomed the release of the report.

He said it had "confirmed that neither the Saudi government, nor senior Saudi officials, nor any person acting on behalf of the Saudi government provided any support or encouragement for these attacks."

Source: AFP