A US federal appeals court has ruled that Saudi Arabia and four of its princes cannot be held liable in the September 11, 2001, terrorist attacks even if they were aware charitable donations to Muslim groups would be funnelled to al-Qaeda.

The 2nd US Circuit Court of Appeals said the defendants were protected by sovereign immunity and the plaintiffs would need to prove that the princes were intentionally targeting US residents.

Lawsuits seeking billions of US dollars in damages were filed by representatives, survivors and relatives of the victims against foreign governments, charities, financial institutions and individuals believed to have provided support to al-Qaeda.

The plaintiffs claimed the defendants gave money to charities in order to funnel it to terrorist organisations behind the attacks on the World Trade Centre and Pentagon.