A US court has ruled that Saudi Arabia and four of its princes are immune from legal action by victims of the September 11 attacks in the US alleging they provided material support to al-Qaeda.

A Saudi banker and a charity were also to be given immunity from prosecution, a federal appeals court in New York ruled on Thursday.

The ruling, by the Second Circuit Court of Appeals, upheld a 2006 ruling dismissing a claim against the Saudis.

The victims and their families said that because the defendants gave money to charities that in turn gave money to al-Qaeda, they should be held responsible for helping to finance the attacks.

The appeals court found that the defendants were protected under the Foreign Sovereign Immunities Act.

The court also said exceptions to the immunity rule do not apply because Saudi Arabia has not been designated a state sponsor of terrorism by the US state department.

About 3,000 people were killed in the September 11, 2001 attacks on New York and Washington which has been claimed by al-Qaeda.