Former U.S. President Donald Trump on Monday filed a lawsuit against the U.S. congressional committee investigating the deadly January 6 attack on the Capitol, alleging it made an illegal request for his White House records.

In the lawsuit filed in the U.S. District Court for the District of Columbia, Trump asserts that materials sought by the House of Representatives' January 6 Select Committee are covered by a legal doctrine known as "executive privilege," which protects the confidentiality of some communications between White House officials.

"The Committee's requests are unprecedented in their breadth and scope and are untethered from any legitimate legislative purpose," Trump's lawyer Jesse Binnall wrote in the lawsuit.

The challenge will likely touch off an extended high-stakes showdown in the courts that will test the constitutional authority of Congress to scrutinize the executive branch.

Executive privilege

Thousands of Trump supporters stormed the Capitol nine months ago in an effort to overturn U.S. President Joe Biden's election victory.

They had been egged on by Trump, whose fiery speech earlier that day falsely claiming election fraud was the culmination of months of baseless claims about a contest he lost fairly to Biden. More than 600 people now face criminal charges stemming from the event.

"The committee's request amounts to nothing less than a vexatious, illegal fishing expedition openly endorsed by Biden and designed to unconstitutionally investigate President Trump and his administration," said the lawsuit filed in Washington's district court.

Many legal experts have said Trump, as the former president, cannot lawfully use executive privilege to block the House panel's requests for documents and testimony.

Trump was impeached by the Democratic-led House on a charge of inciting the attack on the Capitol in a fiery speech at a rally earlier that day. However, the Senate acquitted him.

Earlier this month, Biden authorized the National Archives, a government agency that holds records from Trump's time in office, to turn over an initial batch of documents requested by the select committee.

The National Archives has said it will turn over the requested documents to Congress next month, according to Trump's lawsuit, which seeks an injunction halting that process.

Michael Stern, a former congressional lawyer, said Trump's strategy may be to use litigation to stall the select committee's work.

"If he is willing to pay for the lawyers, Trump could delay the production of records for some time," Stern said.

The January 6 committee has also issued subpoenas demanding testimony from Trump advisers, including political strategist Steve Bannon.

Bannon has refused to provide testimony until Trump's assertion of executive privilege has been resolved by a court or through negotiations with the committee.

Last week, the committee said it would formally ask the U.S. Justice Department to bring criminal charges against Bannon for defying the subpoena.

The committee has subpoenaed other officials, including former Justice Department official Jeffrey Clark, Trump's former chief of staff Mark Meadows, deputy chief of staff Dan Scavino and former Defense Department official Kash Patel.

(With input from agencies)