Former United States Republican party presidential candidate Mitt Romney, after a three-week flirtation with another run for president, has definitively said that he will not seek the White House in 2016.

"After putting considerable thought into making another run for president, I've decided it is best to give other leaders in the party the opportunity to become our next nominee," the Republican Party's 2012 nominee said in a statement on Friday.

As Romney sounded out his former team about putting together a new national campaign, he discovered that several of his past fundraisers had already made plans for 2016 and were committed to supporting former Florida Governor Jeb Bush, the brother and son of former presidents.

The Associated Press news agency reported that several key former Romney donors said that in Bush they see someone who can successfully serve as president, as they believe Romney could. But they also think Bush has the personality and senior staff needed to win the White House, something the former Massachusetts governor could not bring together in his two previous presidential campaigns.

The former governor of Massachusetts had jumped back into the presidential discussion on January 10, when he surprised a small group of former donors at a meeting in New York by telling them he was eyeing a third run for the White House.

It was a monumental change for Romney, who since losing the 2012 election to President Barack Obama had repeatedly told all who asked that his career in politics was over and that he would not again run for president.

The exit of Romney from the upcoming campaign most immediately benefits the other favourites of the party's establishment wing, including Bush, New Jersey Governor Chris Christie, Florida Senator Marco Rubio and Wisconsin Governor Scott Walker.

The more conservative side of the field is largely unchanged, with a group of candidates that will likely include Kentucky Senator Rand Paul, Texas Senator Ted Cruz and former Arkansas Governor Mike Huckabee.

Romney's aides had acknowledged a third campaign would have been more difficult than his second, but insisted he would have had the necessary financial support, noting his supporters raised more than $1bn during the 2012 election.