Washington DC - Supreme Court Justice Samuel Alito is facing calls to recuse himself from cases involving Donald Trump after an inverted American flag – a symbol of the ex-president's false election fraud claims – was flown outside his home.

A January 2021 photo of the upside-down flag outside the Alexandria, Virginia house of archconservative judge was published by The New York Times on Thursday.

The report has intensified scrutiny of the nation's highest court as it prepares to rule on the scope of the former president's immunity from prosecution.

In a statement to the newspaper, the 74-year-old Alito said he "had no involvement whatsoever in the flying of the flag," which was displayed in the weeks following the January 6 storming of the Capitol by Trump supporters in 2021.

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Alito said the flag was "briefly" flown by his wife "in response to a neighbor's use of objectionable and personally insulting language on yard signs."

Another staunch conservative justice, Clarence Thomas, has also been the target of recusal demands because of his wife's involvement with efforts to block Democrat Joe Biden's 2020 election victory.

Thomas, who is the longest-serving justice on the court, has refused to step aside from Trump-related cases and recently described the nation's capital as an "awful place" full of "nastiness" and "lies."

Democratic Senator Dick Durbin, chairman of the Senate Judiciary Committee, said Alito should "recuse himself immediately from cases related to the 2020 election and the January 6th insurrection."

"Flying an upside-down American flag – a symbol of the so-called 'Stop the Steal' movement – clearly creates the appearance of bias," Durbin said.

"The Court is in an ethical crisis of its own making, and Justice Alito and the rest of the Court should be doing everything in their power to regain public trust," Durbin said. "Supreme Court justices should be held to the highest ethical standards, not the lowest."

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Another Democratic senator, Richard Blumenthal of New Jersey, told MSNBC the flag report left him "beyond disturbed."

Blumenthal said Chief Justice John Roberts "has to tell these two justices that they have no business sitting on" Trump cases.

Asked about the Alito controversy, White House Press Secretary Karine Jean-Pierre said: "We should be respecting that flag."

"I cannot speak to if he should recuse himself," Jean-Pierre added. "That is for the court to decide."

The Supreme Court heard Trump's claim on April 25 that as a former president, he is immune from criminal prosecution.

The Republican had been scheduled to go on trial in Washington on March 4 on charges of seeking to overturn the 2020 election, but the case has been on hold pending a ruling by the Supreme Court on the immunity question.

A ruling is expected by the end of June or early July, but it is unlikely a trial can take place before November, when the 77-year-old is expected to take on Biden in a rematch of their 2020 White House race.

The Supreme Court adopted an ethics code in November of last year following a series of scandals over lavish gifts and luxury vacations received by Thomas and Alito, both of whom have denied any impropriety.

The nine members of the court, three of whom were appointed by Trump, are the only federal judges not explicitly subject to ethical oversight, and pressure had been mounting from Senate Democrats for them to accept a set of standards.