DES MOINES, Iowa — At least $12.5 million and counting has blanketed the airwaves ahead of next Tuesday's Republican presidential caucuses, with hard-hitting commercials awash in ghoulish images and startling claims. Most are coming from a proliferation of new independent groups aligned with the candidates.

To hear the ads tell it, Newt Gingrich is a "serial hypocrite," Rick Perry "double dips" as governor and the "liberal Republican establishment" is plotting to anoint Mitt Romney as the party's presidential nominee. The attacks, the bulk of the commercials on the air, reflected the volatile state of the race five days before the first votes of the GOP presidential nominating contest.

After a slow start, the ads in Iowa are coming on fast and furious.

On Thursday alone, at least four new commercials were rolled out, including one by Perry castigating his rivals as Washington insiders and saying: "The fox guarding the henhouse is like asking a congressman to fix Washington: bad idea." An outside group aligned with Romney, Restore Our Future, rolled out a new spot that criticizes Gingrich and asks: "Haven't we had enough mistakes?"

In the final days of the Iowa campaign, most of the ads are deeply negative, thanks in large part to the proliferation of outside groups, known as super PACs, that are doing the dirty work for candidates they support. Gingrich has been the biggest target, withering under attacks from Ron Paul and Rick Perry's campaign as well as from several outside groups like the one aligned with Romney. Polls show that Gingrich's standing in Iowa has slid accordingly.

"I call it ad wars whack-a-mole — this endless attacking in all directions, trying to slam down anyone who is surging to the top," said David Perlmutter, a University of Iowa journalism professor who studies political communication. "This is the most negative I've ever seen it. The ads are so blatantly negative I would have told you 10 years ago this would never fly in Iowa."

It's a different landscape in the campaign advertising world than four years ago when Barack Obama won Iowa's Democratic caucuses and Mike Huckabee carried the Republican side. Social media has intensified the advertising binge, with many spots debuting on TV but also going viral across the web at almost no cost to the campaigns that sponsor them. Candidates are making heavy use of online advertising to target voters based on location and other demographic information.

Campaigns are also producing video specifically for the YouTube audience, like a new 90-second Romney video excerpting a speech Obama delivered in Iowa days before winning the Democratic caucuses in 2008.

"Well, Mr. President, you've had your moment ... this is our time," Romney says in the spot.

On Thursday, Jon Huntsman's campaign — which can't afford to put commercials on TV and is competing only in New Hampshire — hit at Paul in a new web video that highlights comments about race and gays in newsletters Paul used to put out. The ad asks: "Can New Hampshire voters really trust Ron Paul?'"

But nothing has altered the environment more than super PACs, which are facing their first test in a presidential campaign since a Supreme Court decision two years ago eased restrictions on campaign spending by corporations, unions and individuals.

Much of $12.5 million spent to date in Iowa, a figure confirmed by ad tracking firms, outside groups and the GOP campaigns, has been spent in just the past few weeks, much of it paying for negative ads.

The pro-Romney super PAC, Restore Our Future, has been by far the most influential in Iowa, helping to bolster the former Massachusetts governor's position in the state he lost in 2008, crippling that campaign.

The group formed by Romney allies has spent at least $2.7 million in the state. The vast majority has been used to trash Gingrich, the former House speaker whose sudden surge in the polls earlier this month has been summarily halted in recent days. In ad after ad, Romney's allies have berated Gingrich for ethical "baggage," accepting $1.6 million in consulting fees from federal mortgage giant Freddie Mac and pledging to tackle climate change in an ad with House Democratic Leader Nancy Pelosi.

Another new ad from the group goes after both Gingrich and Perry for being "liberal on immigration."

Perry, the Texas governor, has defended his state's policy of allowing the children of illegal immigrants to pay in-state tuition rates at public universities, while Gingrich has spoken out against deporting those who have lived in the U.S. for many years without permission to be in the country.

The ad also chides Perry for taking advantage of a loophole in state law that allows him to supplement his governor's salary with his $90,000 annual pension, even as Perry has used his own ads to rail against congressional salaries.

Romney has stepped up his advertising presence in Iowa, driving a largely positive message while his allies have made it easy for him to avoid attacking his Republican rivals.

"In the campaign to come, the American ideals of economic freedom and opportunity need a clear and unapologetic defense. And I intend to make it because I have lived it," Romney says in a new uplifting 60-second commercial he began airing Thursday.

Gingrich, for his part, has railed against the Romney allies' ad blitz but has refused to respond in kind. A pro-Gingrich super PAC has begun fighting back, running ads in Iowa claiming the Republican establishment is "attacking him with falsehoods."

The ad warns: "Don't let the liberal Republican establishment pick our candidate."

But the assist from the pro-Gingrich group Winning Our Future may be too little, too late. A new CNN-Time poll found Gingrich now in fourth place in Iowa, behind Romney, Paul and Rick Santorum.

Other Republican hopefuls have super PACs that support them, including Perry and Santorum. The former Pennsylvania senator has run no ads of his own but has seen his position in Iowa strengthen in recent days in part by $327,000 in ad spending from a super PAC called the Red White and Blue Fund.

Our Destiny, a super PAC backing Huntsman, has run ads in New Hampshire for the former Utah governor. Huntsman is skipping the Iowa caucuses to focus on New Hampshire, which holds the nation's first primary on Jan. 10.

Perry has run the most campaign ads in Iowa, spending at least $3.9 million so far. His ads have offered a smattering of sometimes conflicting messages — promoting his conservative Christian faith in one to calling for a part-time Congress in another.

"I'm an outsider who will overhaul Washington," Perry says in his latest ad, while pledging anew to end "Obama's war on religion."

Make Us Great Again, a pro-Perry super PAC, has also been on the air for weeks in Iowa.

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The heavy spending hasn't seemed to help Perry much — polls have consistently shown him trailing in the state, though he has gained some ground.

Paul has also been on the air for months and has not been shy about hitting his opponents. His latest ad, titled "Washington Machine," hits Gingrich as a "serial hypocrite" and Romney as a "flip flopper."

Cash strapped and struggling in polls, Michele Bachmann will run TV commercials a day before the caucuses. Her campaign has run radio ads and she's sought free media on a bus tour through Iowa's 99 counties.

Associated Press writers Brian Bakst in Iowa and Jack Gillum in Washington contributed to this report.