US President Donald Trump and 17 US states have thrown their support behind a long-shot lawsuit by Texas seeking to overturn his election loss by asking the US Supreme Court to throw out voting results in four states.

Mr Trump, defeated by president-elect Joe Biden in the November 3 election, filed a motion with the court asking the nine justices to let him intervene and become a plaintiff in the suit filed on Tuesday (local time) by Republican-governed Texas against Georgia, Michigan, Pennsylvania and Wisconsin.

If the justices let Mr Trump join, it would create the extraordinary circumstance of a sitting US president asking the top American court to decide that the millions of votes cast in the four states did not count.

Mr Trump lost to Mr Biden in the four election battleground states after winning them in 2016.

Writing on Twitter, Mr Trump said, “This is the big one. Our Country needs a victory!”

Tweet from @realDonaldTrump

In a separate brief, lawyers for 17 states led by Missouri’s Republican Attorney-General Eric Schmitt also urged the justices to hear the case.

Election law experts have said the Texas lawsuit stands little chance of success.

The lawsuit, the latest in a series of challenges brought by Trump’s campaign and supporters that so far have failed in numerous courts, was brought by Ken Paxton, Republican attorney-general of Texas.

With Missouri, the states joining Texas are: Alabama, Arkansas, Florida, Indiana, Kansas, Louisiana, Mississippi, Montana, Nebraska, North Dakota, Oklahoma, South Carolina, South Dakota, Tennessee, Utah and West Virginia.

All are represented by Republican officials in the filing. All but three have Republican governors.

Mr Trump has falsely claimed he won re-election and has made baseless allegations of widespread voting fraud. Election officials at the state level have said they have found no evidence.

Officials from Georgia, Michigan, Pennsylvania and Wisconsin have called the lawsuit a reckless attack on democracy.

It was filed directly with the Supreme Court rather than a lower court, as is permitted for certain litigation.

The New York Times, quoting an unnamed source, reported Trump has asked Republican US Senator Ted Cruz of Texas to argue the case if the Supreme Court agrees to hear it.

“Both procedurally and substantively, it’s a mess,” Justin Levitt, an election law professor at Loyola Law School in California, said of the Texas lawsuit.

“There’s zero chance the court agrees to take the case.”

The Texas suit argued that changes made by the four states to voting procedures amid the coronavirus pandemic to expand mail-in voting were unlawful.

Texas asked the Supreme Court to immediately block the four states from using the voting results to appoint presidential electors to the Electoral College.

-AP