Washington DC - President Joe Biden said Wednesday he was "not focused" on an impeachment inquiry announced a day earlier by Republican lawmakers, as his White House blasted "baseless" allegations of wrongdoing.

"I don't know quite why, but they just knew they wanted to impeach me," Biden said of the Republican effort.

"I get up every day... not focused on impeachment. I've got a job to do. I've got to deal with the issues that affect the American people every single solitary day," he told attendees at a private campaign fundraiser.

The 80-year-old Democrat's brief remarks were his first public comments on the issue since House Speaker Kevin McCarthy, the top Republican in Congress, bowed to intense pressure from his party's hard right and authorized the impeachment inquiry on Tuesday.

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When asked about the investigation earlier Wednesday, White House Press Secretary Karine Jean-Pierre had stronger words.

"They have spent all year investigating the president... and have turned up with no evidence, none, that he did anything wrong," she told reporters. "That's because the president didn't do anything wrong."

But Jean-Pierre said Republicans did not even have enough support for a vote in the House to approve an impeachment probe.

"Even House Republicans have said the evidence does not exist," she said. "This is a political stunt."

The probe comes as Biden faces low poll ratings ahead of a likely rematch with former president Donald Trump – who himself was impeached twice by a Democratically controlled House but acquitted in the Senate – in next year's presidential election.