Obama told CBS News ahead of his trip that he was "opposed" to the bipartisan bill, which would potentially allow the royal Saudi government to be sued in American courts over the September 11, 2001 attacks.

The "Justice Against Sponsors of Terrorism Act" was drafted following claims by Zacarias Moussaoui, dubbed the 20th hijacker, that members of the Saudi royal family donated millions of dollars to Al-Qaeda in the 1990s.

The bill would essentially remove the right of sovereign immunity so that "if you basically fund and sponsor terrorist attacks on American soil, you can be liable for damages," said main co-sponsor Senator John Cornyn, the chamber's number two Republican.

The draft legislation has caused outrage in Riyadh, with Saudi officials warning that they would sell off several hundred billion dollars in American assets if Congress passes the measure. The forced sale would take place to avoid having the assets frozen by US courts.

Riyadh 'not serious'

But the White House said Monday it was optimistic that Riyadh would not follow through on its threat.

"I'm confident that the Saudis recognize, just as much as we do, our shared interest in preserving the stability of the global financial system," White House spokesman Josh Earnest told reporters.

It's not clear whether Obama will discuss the bill with King Salman and other Saudi officials during his trip, which begins on Wednesday. The visit - for a Persian Gulf summit - is part of a series of international farewell tours that will later take in Berlin and London.

Fifteen of the 19 hijackers on 9/11 were Saudi citizens. But no official Saudi complicity in the terror attacks has been proven, and the kingdom has never been formally implicated.

Family members of victims who were killed in the September 2001 attacks urged Obama to support the legislation and to bring up the issue on his trip.

"It is not acceptable ... to succumb to the demands of a foreign government that we abandon principles of American justice while we pursue our diplomatic goals," they wrote in a letter to the US leader that was released to the media.

Republican presidential candidate Senator Ted Cruz has sponsored the legislation, and Democratic White House hopefuls Hillary Clinton and Senator Bernie Sanders said they favor the bill.

In September, a US judge dismissed claims against Saudi Arabia by families of victims of the attacks, saying the kingdom had sovereign immunity from damage claims.