Barack Obama said every resource was needed to beat John McCain
Democrat Barack Obama has said he will not take public financing, allowing him to raise unlimited private funds in his campaign for the US presidency.
His decision means he will forgo more than $80m (£40.5m) that would have been available for him to fight Republican John McCain for the White House.
Candidates who accept public money cannot raise funds from private donors.
Mr Obama set records raising money for his campaign for the Democratic nomination during the primary contests.
The decision reverses his earlier promise to use the federal public financing system if his Republican rival also did so.
The Obama campaign team said Mr McCain was already using privately-raised funds in his campaign and that the public finance system was "broken".
CAMPAIGN TOTALS SO FAR
Cash on hand: $46m
Cash on hand: $24m
Totals up to and for April 2008
"It's not an easy decision, and especially because I support a robust system of public financing of elections," Mr Obama said in a video message to supporters.
"But the public financing of presidential elections as it exists today is broken, and we face opponents who've become masters at gaming this broken system."
He said Mr McCain's campaign was being financed by Washington lobbyists and special interest groups.
Mr Obama becomes the first presidential candidate not to use the public financing system for a general election since campaign finance laws were overhauled following the Watergate scandal of 1974.
Mr McCain's team however, accused Mr Obama of breaking his promise to take public funding.
"This decision will have far-reaching and extraordinary consequences that will weaken and undermine the public financing system," said Mr McCain's spokeswoman Jill Hazelbaker.
Mr McCain has said he is likely to take the public money.
Mr Obama has so far raised an unprecedented $265m (£134.5m) in donations in his presidential race, most of it from small donations given over the internet.
This dwarfs the nearly $97m Mr McCain has so far raised.
But Mr McCain can draw on the deep pockets of the Republican National Committee, which has far more money than the Democratic National Committee, correspondents say.