Newt Gingrich has decided to quit his long-shot US presidential run and will next week throw his support behind presumptive Republican nominee Mitt Romney, his spokesman said.
Gingrich, a fiery former speaker of the House of Representatives, is expected to hold a final event in Washington on Tuesday May 1, after which he will suspend his White House campaign, which has foundered in recent months.
The New York Times reported that Gingrich telephoned Romney, a former governor of Massachusetts, to tell him that after next week's event he would start working to win voters for his former rival ahead of November's election.
Gingrich's spokesman R.C. Hammond, referring to the call, told the newspaper that "a Republican turnout, especially among conservatives, is key to stopping'' Democratic incumbent Barack Obama winning a second term.
The apparent decision of Gingrich, 68, to end his presidential tilt and step aside came the morning after Romney, 64, effectively claimed the nomination in a five-state sweep of primary contests.
"When he says he is transitioning, what he means is that he is trying to determine as a citizen how he will pro-actively help Mitt Romney become president,'' a Gingrich source told CNN, referring to the decision to quit.
A source told Fox News that Gingrich would "more than likely,'' endorse Romney, a multimillionaire businessman and former venture capitalist who ran a failed campaign to win the Republican nomination in 2008.
After wins Tuesday in Connecticut, Delaware, New York, Pennsylvania and Rhode Island, Romney was free to gear up his general election campaign and directly target Obama after months of tangling with Republican rivals.
Gingrich, who after a slow start briefly led polls in the Republican race, pulled off a dramatic win in the South Carolina primary back in January but that victory never produced the national momentum he hoped it would.
On all-important Super Tuesday in March, Gingrich bagged only one of the 10 states on offer, Georgia in his native south, dimming the hopes of his supporters that he might be able to reinvigorate his White House chances.
With Romney's main rival Rick Santorum already out of the race, Gingrich has been under mounting pressure to stand aside and allow the likely nominee to focus on challenging Obama in the run-up to the November 6 election.
Gingrich's withdrawal would leave only Ron Paul, a Texas congressman who represents the libertarian wing of the party, in the race. Paul consistently placed fourth in the primary season and has no chance of catching Romney.
Gingrich, the Republican Party's self-proclaimed philosopher king and its irascible, erratic showman, displayed in January exactly why he can be such a formidable opponent.
Targeted with the first question of a high-stakes live debate in the heart of America's Bible Belt, he was asked to comment on the bombshell allegation from his ex-wife that he had once requested an open marriage.
With his presidential hopes hanging in the balance, Gingrich struck out at the "destructive, vicious, negative nature of much of the news media,'' saying it was "as close to despicable as anything I can imagine.''
The stunning counter-attack, which played brilliantly to the innate conservative distrust of the liberal media, transformed the former House speaker from villain to hero and recast his campaign.
In the end though, the unexpected surge of conservative rival Santorum, a 53-year-old former Pennsylvania senator, stole a lot of the fire from Gingrich's campaign.
Santorum, a Catholic and fervent opponent of abortion and gay marriage, enjoyed success in the South and the Midwest, splitting the conservative vote and making it incredibly hard for Gingrich to realistically challenge Romney.