Washington: Saudi Arabia has told the Obama administration and members of the Congress that it will sell off hundreds of billions of dollars worth of American assets held by the kingdom if the Congress passes a bill that would allow the Saudi government to be held responsible in US courts for any role in the September 11, 2001, attacks.

The Obama administration has lobbied the Congress to block the bill’s passage, according to administration officials and Congressional aides from both parties, and the Saudi threats have been the subject of intense discussions in recent weeks between lawmakers and officials from the State Department and the Pentagon. The officials have warned senators of diplomatic and economic fallout from the legislation.

Adel Al Jubeir, the Saudi foreign minister, delivered the kingdom’s message personally last month during a trip to Washington, telling lawmakers that Saudi Arabia would be forced to sell up to $750 billion in treasury securities and other assets in the US before they could be in danger of being frozen by US courts.

Several outside economists are sceptical that the Saudis will follow through, saying that such a sell-off would be difficult to execute and would end up crippling the kingdom’s economy. But the threat is another sign of the escalating tensions between Saudi Arabia and the US.

The administration, which argues that the legislation would put Americans at legal risk overseas, has been lobbying so intently against the bill that some lawmakers and families of September 11 victims are infuriated. In their view, the Obama administration has consistently sided with the kingdom and has thwarted their efforts to learn what they believe to be the truth about the role some Saudi officials played in the terror plot.

“It’s stunning to think that our government would back the Saudis over its own citizens,” said Mindy Kleinberg, whose husband died in the World Trade Center on September 11 and who is part of a group of victims’ family members pushing for the legislation.

US President Barack Obama will arrive in Riyadh on Wednesday for meetings with King Salman and other Saudi officials. It is unclear whether the dispute over the September 11 legislation will be on the agenda for the talks.

A spokesman for the Saudi embassy did not return a message seeking comment.

Saudi officials have long denied that the kingdom had any role in the September 11 plot, and the 9/11 Commission found “no evidence that the Saudi government as an institution or senior Saudi officials individually funded the organisation.” But critics have noted that the commission’s narrow wording left open the possibility that less senior officials or parts of the Saudi government could have played a role. Suspicions have lingered, partly because of the conclusions of a 2002 congressional inquiry in the attacks that cited some evidence that Saudi officials living in the United States at the time had a hand in the plot.

Those conclusions, contained in 28 pages of the report, still have not been released publicly.

The dispute comes as bipartisan criticism is growing in Congress about Washington’s alliance with Saudi Arabia, for decades a crucial US ally in the Middle East and half of a partnership that once received little scrutiny from lawmakers. Last week, two senators introduced a resolution that would put restrictions on US arms sales to Saudi Arabia, which have expanded dramatically during the Obama administration.

Families of the September 11 victims have used the courts to try to hold members of the Saudi royal family, Saudi banks and charities liable because of what the plaintiffs charged was Saudi financial support for terrorism. These efforts have largely been stymied, in part because of a 1976 law that gives foreign nations some immunity from lawsuits in US courts.

The Senate bill is intended to make clear that the immunity given to foreign nations under the law should not apply in cases where nations are found culpable for terrorist attacks that kill Americans on US soil. If the bill were to pass both houses of Congress and be signed by the president, it could clear a path for the role of the Saudi government to be examined in the September 11 lawsuits.

Obama administration officials counter that weakening the sovereign immunity provisions would put the US government, along with its citizens and corporations, in legal risk abroad because other nations might retaliate with their own legislation. Secretary of State John Kerry told a Senate panel in February that the bill, in its current form, would “expose the United States of America to lawsuits and take away our sovereign immunity and create a terrible precedent.”

The bill’s sponsors have said that the legislation is purposely drawn very narrowly — involving only attacks on US soil — to reduce the prospect that other nations might try to fight back.

In a closed-door briefing on Capitol Hill on March 4, Anne W. Patterson, an assistant secretary of state, and Andrew Exum, a top Pentagon official on Middle East policy, told staff members of the Senate Armed Services Committee that US troops and civilians could be in legal jeopardy if other nations decide to retaliate and strip Americans of immunity abroad. They also discussed the Saudi threats specifically, laying out the impacts if Saudi Arabia made good on their economic threats.

Edwin M. Truman, a fellow at the Peterson Institute for International Economics, said he thought the Saudis were likely making an “empty threat.” Selling hundreds of billions of dollars of American assets would not only be technically difficult to pull off, he said, but it likely would cause global market turmoil for which the Saudis would be blamed.

Moreover, he said, it could destabilise the American dollar — the currency to which the Saudi riyal is pegged.

“The only way they could punish us is by punishing themselves,” Truman said.

The bill is an anomaly in a Congress fractured by bitter partisanship, especially during an election year. It is sponsored by Sen. John Cornyn, R-Texas, and Senator Charles E. Schumer, D-N. Y. It has the support of an unlikely coalition of liberal and conservative senators, including Al Franken, D-Minn., and Ted Cruz, R-Texas. It passed through the Judiciary Committee in January without dissent.

“As our nation confronts new and expanding terror networks that are targeting our citizens, stopping the funding source for terrorists becomes even more important,” Cornyn said last month.

The alliance with Saudi Arabia has frayed in recent years as the White House has tried to thaw ties with Iran — Saudi Arabia’s bitter enemy — in the midst of recriminations between American and Saudi officials about the role that both countries should play in the stability of the Middle East. Last month, The Atlantic published an article based on interviews with Obama, who told the author, Jeffrey Goldberg, that the Saudis need to “share the neighbourhood” with their Iranian rivals.

But the administration has supported Saudi Arabia on other fronts, including providing the country with targeting intelligence and logistical support for its war in Yemen. The Saudi military is flying jets and dropping bombs it bought from the US — part of the billions of dollars in arms deals that have been negotiated with Saudi Arabia and other Gulf nations during the Obama administration.

The war has been a humanitarian disaster and fuelled a resurgence of Al Qaida in Yemen, leading to the resolution in Congress to put new restrictions on arms deals to the kingdom. Sen. Christopher S. Murphy, D-Conn., one of the resolution’s sponsors and a member of the Senate Foreign Relations Committee, said that Congress has been “feckless” in conducting oversight of arms sales, especially those destined for Saudi Arabia.

“My first desire is for our relationship with Saudi Arabia to come with a greater degree of conditionality than it currently does,” he said.