A spokesman for Newt Gingrich says the former U.S. House speaker will officially end his campaign for the Republican presidential nomination next week.

The spokesman says Gingrich will endorse Mitt Romney, the party's presumptive nominee, when he suspends his campaign. Romney called Gingrich Wednesday, a day after Romney won five state primary elections to effectively seal the nomination.

Gingrich acknowledged that Romney is the likely nominee during a campaign appearance Wednesday in North Carolina.

“This guy's worked six years, put together a big machine, and has put together a serious campaign. I think obviously that I would be a better candidate, but the objective factor is that voters didn't think that. I also think that it's very, very important that we be unified. Nothing should stop, no conservative anywhere in America should have any doubt about the importance of defeating Barack Obama.”

Gingrich emerged as a strong contender after winning the South Carolina primary in January, but his campaign faltered after he lost the following primary in Florida. His only other primary election win was in March, in his home state of Georgia, and his campaign is over $4 million in debt.

Gingrich's spokesman says he will focus his efforts on helping Republicans retain control of the U.S. House of Representatives and seize control of the Senate. Gingrich masterminded the Republican takeover of the House in 1994.

Another former Republican presidential candidate, Texas Governor Rick Perry, announced Wednesday that he was endorsing Romney. Perry dropped out of the race after the South Carolina primary and had endorsed Gingrich for the nomination.

Meanwhile, a spokesman for President Barack Obama's campaign announced Wednesday that the president will officially begin his re-election campaign next week with rallies in Virginia and Ohio, accompanied by his wife Michelle.

Mr. Obama had no challengers for the Democratic Party nomination.