The House of Representatives had approved the act on Friday, four months after the Senate had passed it and just two days before the 15th anniversary of the attacks on US soil, which killed nearly 3,000 people.

But Obama's staff on Monday confirmed that the bill to allow relatives of victims of the 2001 attacks to sue Saudi Arabia for compensation would be vetoed by the president. "I do anticipate the president would veto this legislation when it is presented to him," spokesman Josh Earnest said.

"That's not an effective, forceful way for us to respond to terrorism," Earnest said. He said that the text has yet to reach the president's desk.

Staunch opposition

The act has raised major concerns among US allies in the Gulf States. Saudi Arabia was the home nation to 15 of the 19 hijackers.

The six-member Gulf Cooperation Council, made up of Bahrain, Kuwait, Oman, Qatar, Saudi Arabia, and the United Arab Emirates, expressed on Monday "profound worry" over the bill, claiming it would "create a grave precedent."

If passed, the bill would have waived the doctrine of sovereign immunity that protects nation states fom civil suits or criminal prosecution. This could have exposed the US to lawsuits in a number of countries.

"There's no denying the political potency of this issue. But the president believes that it's important to look out for our country, to look out for our service members and look out for our diplomats," Earnest said. "And allowing this bill to come into law would increase the risk that they face."

Should Congress wish to override the veto, it would require a two-thirds vote in both the House and Senate. It would also be the first time that Obama would have faced such a move.

Obama has 10 days to veto the bill before it automatically becomes law. The Constitution also allows a "pocket veto." Under this, a president can defeat a bill just by holding onto it until Congress is out of session.

jm/gsw (Reuters, AFP, AP)