The only al-Qaeda plotter who has been convicted over the 9/11 attacks has claimed the Saudi royal family financially supported the al-Qaeda.

Speaking to American lawyers in 127 pages of transcript, French-born Zacarias Moussaoui, dubbed the "20th hijacker", claims Saudi donations of up to two to three million dollars were "crucial" to al-Qaeda in the late 1990s.

According to Moussaoui, al-Qaeda mastermind Osama bin Laden was in direct contact with several senior Saudi officials.

Moussaoui alleges he met an official from the Saudi embassy in Washington DC in Afghanistan and discussed al-Qaeda's plots to attack the United States.

He claims he was supposed to meet the same official again in Washington to help him shoot down Air Force One.

Moussaoui also claims he created a database of al-Qaeda donors, which included royal family members, like Prince Bandar bin Sultan who served as the Saudi ambassador to the US for 22 years until 2005, reported France24 News.

The Saudi embassy in Washington, however, denies all claims.

Referring to Moussaoui as, "a deranged criminal whose own lawyers presented evidence that he was mentally incompetent," the Saudi embassy said in a statement that Moussaoui's words have no credibility.

"The September 11 attack has been the most intensely investigated crime in history and the findings show no involvement by the Saudi government or Saudi officials," said the statement.

Moussaoui has pleaded guilty to plotting the 9/11 attack and is presently held at a prison in Colorado.

Zacarias Moussaoui
A man watchs on his computer\'s screen a TV programm displaying the transfer of French Zacarias Moussaoui, the only person convicted in the September 11, 2001 terrorist attacks against the United States. Getty Images