WASHINGTON - U.S. President Barack Obama welcomed Mitt Romney to the White House on Thursday as the two men sat down for a private lunch less than a month after their bruising election battle.

Romney was whisked onto the White House grounds in a dark SUV just after noon; a crush of television cameras captured his entrance to the president's home. He was alone and smiled as he entered the White House.

Obama and Romney dined in the White House private dining room after the president made good on a promise made during his victory speech on Nov. 6 to reach out to his one-time rival for the White House.

Their lunch was closed to the media — not even a pool photographer was allowed in, likely at Romney's request. When Obama sat down with John McCain for a similar lunch in Chicago in 2008, the two men posed for photographers.

Romney has been in near-seclusion at his home in southern California since losing the election he felt certain he would win.

Several of his campaign aides have said they were convinced of victory on Nov. 6, believing Obama's re-election team was over-estimating how many of the president's core supporters would actually get out and vote.

Indeed, by late afternoon on election day, Romney told reporters on his campaign plane that he'd written just one speech ahead of the polls closing: a 1,100-word victory speech. His delay in taking the stage after Obama was declared the winner was reportedly due to his need to pen a quick concession address.

Romney, 65, has made headlines only once since his defeat, when he told a conference call of supporters that he'd lost the election because he couldn't compete with the "gifts" Obama offered to his own constituents —minorities, youth and women chief among them.

While he's ruled out ever running for public office again, he's reportedly expressed interest in philanthropic efforts or having another role in future Olympics after successfully helming the Salt Lake City Games in 2002.

Obama wants to hear Romney's ideas for making government more efficient, the White House said in advance of the lunch. The president has floated the idea of merging some business-related government agencies and has asked Congress for the go-ahead to re-organize some of the executive branch.

His encounter with Romney also comes as Obama attempts to reach a deal with congressional Republicans on the looming so-called "fiscal cliff" that threatens to push the U.S. economy back into a recession.

Obama has been arguing forcefully in favour of tax hikes on wealthy Americans while extending tax cuts for the middle class. Romney bitterly disputed that approach on the campaign trail, saying the George W. Bush-era tax cuts should be extended for all Americans, including the wealthy.

The two men barely know one another, meeting only fleetingly prior to the 2012 election. Their primary interaction was the three presidential debates, at least two of which were heated and hostile.

The Obama campaign repeatedly portrayed Romney as a callous rich man looking out only for the wealthy, while the Republican painted Obama as a hapless economic failure.

Earlier Thursday, Romney met with Paul Ryan, his former running mate. The Wisconsin congressman is heavily involved in the so-called fiscal cliff negotiations under way on Capitol Hill.

"I remain grateful to Governor Romney for the honor of joining his ticket this fall, and I cherish our friendship," Ryan said in a statement following their meeting.

"I'm proud of the principles and ideas we advanced during the campaign and the commitment we share to expanding opportunity and promoting economic security for American families."