Michael Bloomberg served as mayor of New York City from 2002 to 2013. He switched his party affiliation from Republican to independent in 2007. (Reuters file photo)
Former New York Mayor Michael Bloomberg said on Monday he would not mount an independent bid for the US presidency, and criticized Democratic and Republican candidates for catering to the fringes of their parties.
A billionaire media mogul who combined business-friendly fiscal policies with liberal views on gun control and other social issues, Bloomberg could have potentially appealed to centrist voters in a year when candidates from the far left and far right of the political spectrum have gained traction.
But he said he worried that a three-person race would increase the changes that either Republican front-runner Donald Trump or his party rival US Senator Ted Cruz could win the White House.
"That is not a risk I can take in good conscience," he wrote on Bloomberg View, an opinion Web site that is part of his media empire.
Bloomberg never received much interest from American voters.
About 12 per cent of likely voters said they would support him in a three-way race for president with Democrat Hillary Clinton and Trump, according to a Reuters/Ipsos national poll from March 2 to 7.
Another 41 per cent said they would support Clinton and 31 per cent said they would support Trump. The poll of 1,695 likely voters has a credibility interval of 3 percentage points.
Bloomberg said Trump, a billionaire real estate mogul who is leading the battle to win the Republican nomination for the November 8 election, has backed policies that would undermine religious tolerance and threaten national security.
"He has run the most divisive and demagogic presidential campaign I can remember, preying on people's prejudices and fears," Bloomberg wrote. He said Cruz, a conservative from Texas, was divisive as well.
Bloomberg also hit out at Clinton and her rival for the Democratic nomination, US Senator Bernie Sanders from Vermont, for criticizing free trade and the financial industry.
"Extremism is on the march, and unless we stop it, our problems at home and abroad will grow worse," he wrote.
Spokespeople for Trump and Cruz did not immediately respond to requests for comment about Bloomberg's criticism.
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