Former New York mayor Rudy Giuliani has officially dropped out of the Republican race and endorsed Sen. John McCain, hours after John Edwards abandoned his bid for the Democratic party's nomination.

"Today I am officially announcing my withdrawal as a candidate for president of the United States," Giuliani said in Simi Valley, Calif.

"John McCain is the most qualified candidate to be the next commander-in-chief of the United States."

Giuliani, an early front-runner among the Republican field, adopted an unorthodox strategy of skipping the early primaries to focus on winning Florida, the biggest state of the pre-"Super Tuesday" primaries to be held on Feb. 5.

However, he finished third with 15 per cent of the vote, well behind former Massachusetts governor Mitt Romney, with 31 per cent support, and McCain, who won with 36 per cent support.

Giuliani had run mainly on the profile he gained as New York's mayor during the terror attack of Sept. 11, 2001. He had promised to be tough on so-called "war on terror" issues.

Edwards drops out

Earlier Wednesday, Edwards said he would leave the Democratic presidential race so that "history can blaze its path."

Edwards, a longtime campaigner against poverty, announced his decision in New Orleans' Lower 9th Ward, the same neighbourhood where he announced his candidacy 13 months ago.

The area was destroyed by Hurricane Katrina, but is currently being rebuilt.

"I began my presidential campaign here to remind the country that we as citizens and as a government have a moral responsibility to each other and what we do together matters," Edwards said, his wife Elizabeth and children standing by his side.

"We must do better if we want to live up to the great promise of this country that we all love so much."

Edwards, whose campaign slogan has been "giving a voice to the voiceless," talked about stopping at a New Orleans bridge, where dozens of homeless people sleep every night, while on his way to make the announcement.

He said a woman came up to him as he was leaving the site.

"She said 'you won't forget us will you?' Promise you won't forget us.' Well I say to her and to everyone else struggling to survive in this country, we will never forget you," Edwards said.

He called on his supporters not to give up on the causes that his campaign has stood for, including fighting for the rights of the poor and bringing U.S. troops home from Iraq.

Edwards didn't endorse either of the leading contenders for the nomination, saying it was only certain that history would be made.

"It's time for me to step aside so that history can blaze its path. We don't know who will take the final steps to 1600 Pennsylvania Avenue, but what we do know is our Democratic Party will make history."

The South Carolina-born Edwards finished well behind Illinois Sen. Barack Obama and New York Sen. Hillary Clinton in his home state primary on Saturday. Edwards won that primary in 2004.

He hadn't won any of the early primaries so far.

With files from The Associated Press