Mitt Romney's presidential campaign has raised at least $100 million in August, The Associated Press has learned, hitting that mark for a third consecutive month with a fundraising prowess that has let him outraise President Barack Obama so far this summer.

The early numbers, which include money raised by the national Republican Party, will be publicly released next week. They were described by two people familiar with the figures who spoke on condition of anonymity because they were not authorized to share internal campaign matters.

The numbers were revealed on the first day of the Democratic National Convention in Charlotte, N.C., where delegates will nominate Obama for a second term. Federal records show that Romney and the GOP have pulled in more cash than Obama's re-election effort in May, June and July, including money collected by the Democratic Party.

It is usually difficult for a challenger to raise more money than an incumbent holding a major elective office, particularly in a presidential race.

The figures exclude tens of millions of dollars that outside "super" political action committees are pouring into the race to help Romney. Those groups have been largely bankrolled by wealthy Americans, thanks to changes in recent years that have loosened campaign-finance regulations.

The fundraising news further underscores the problem Obama's campaign may have in staying above water on the money side. While once a record-breaker _ Obama raised a remarkable $750 million four years ago _ the president's advisers are now publicly acknowledging the incumbent likely will be outspent.

Obama and the Democratic Party have not released their August fundraising figures.

Money is a crucial bellwether in presidential campaigns. It costs millions of dollars to run pricey television ads, pay staffers, keep field offices open and conduct get-out-the-vote efforts. Spending by campaigns, parties, super PACs and other outside groups will likely approach $2 billion by November.

Romney and the GOP raised a combined $101 million in July, $106 million in June and $76.8 million in May. For their part, Obama and the Democrats pulled in $75 million last month, and $71 million in June and $60 million in May. Last month, Obama's campaign spent much of its cash _ about $59 million _ on advertising and paid staff.

Pro-Romney super PACs like American Crossroads and Restore Our Future have spent tens of millions of dollars on TV ads critical of Obama in key states, and the groups expect to spend much more as November approaches. Obama also has super PACs working in his favor, although the groups have yet to catch up to the fundraising benchmarks of their GOP counterparts.

All told, the groups' fundraising strength means Romney could have a permanent financial advantage over Obama. An Obama campaign spokesman declined to comment Tuesday.

Romney fundraising officials have told donors there were few states that haven't broken fundraising efforts. That could put Romney on track to raise $800 million by Election Day.

Both campaigns' financial reports detailing sources of revenue and where the money is spent are due to the Federal Election Commission by Sept. 20.

The fundraising figure was first reported by Politico.

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Beaumont reported from Des Moines, Iowa.

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