US presidential hopefuls have been campaigning hard ahead of tight Iowa caucuses, the first big test in the battle for their party's nomination.
Most of the top Republican and Democrat candidates have been crisscrossing Iowa for days, pushing their message home.
The caucuses - simultaneous meetings held at 1,784 locations across the state - will be held on 3 January.
Thousands of political activists have been dispatched by both parties to attend political meetings in the state.
On the Democratic front, a poll for the Des Moines Register gives Barack Obama the backing of 32% among those surveyed, compared to 25% for Hillary Clinton and 24% for John Edwards.
"We just might pull this thing off, Iowa," Mr Obama said in the last of five rallies across Iowa on Monday.
3 Jan: Iowa caucuses
8 Jan: New Hampshire primary
15 Jan: Michigan primary
19 Jan: Nevada caucuses; South Carolina primary (Rep)
26 Jan: South Carolina primary (Dem)
29 Jan: Florida primary
5 Feb: some 20 states including California, New York, New Jersey
A Reuters/C-Span/Zogby poll released at the weekend had given Mrs Clinton a slight lead in Iowa, with Mr Obama and Mr Edwards fighting for second place.
Mr Edwards told voters on Monday that they could choose a different future for America in 2008.
"Let's resolve, tonight, to make this the year that we stood up, took on the corporate greed that has taken over our government, and fought for the better America our children deserve," he said.
But Mrs Clinton, who appeared alongside husband Bill and daughter Chelsea at a New Years Eve rally in Des Moines, said that taking on corporate domination of politics was not "something you have to do by yelling and screaming.
"Save your energy. Get the job done," she said.
Mr Edwards, who polls show has gained momentum in Iowa, was sending out hundreds of volunteers on a state-wide canvass.
Leading candidates have been crisscrossing Iowa
For the Republicans, the poll for the Des Moines Register put former Arkansas Governor Mike Huckabee at 32% and former Massachusetts Governor Mitt Romney at 26%.
The Reuters/C-Span/Zogby poll suggested a tighter contest between the two.
A McClatchy-MSNBC poll, released over the weekend, gave Mr Edwards a single percentage point lead in Iowa over Mrs Clinton, while Mr Romney was just ahead of Mr Huckabee.
"It's about as close as you can get at the top in both races," pollster John Zogby said. "But it's still very uncertain."
Republican John McCain solidified his hold on third place, with former New York Mayor Rudy Giuliani, who has maintained a low-key presence in Iowa, some way behind.
Mr Huckabee announced at a press conference that he would not be using a negative advert about Mr Romney, but showed it to reporters anyway.
In the advert Mr Huckabee was seen saying: "If a man's dishonest to obtain a job, he'll be dishonest on the job. Iowans deserve better."
Mr Romney's camp said the incident raised questions about Mr Huckabee's sincerity.
On Sunday, Mr Huckabee had accused Mr Romney of trying to mislead voters with adverts targeting his record on taxes, illegal immigration and foreign policy views.
"Mitt Romney is running a very desperate and, frankly, a dishonest campaign," Mr Huckabee said on NBC. He also questioned whether Mr Romney could be trusted with the presidency.
For their part, Mr Romney's team accused Mr Huckabee of "testiness and irritability".
In his closing message on the NBC's Meet the Press on Sunday morning Mr Obama acknowledged that the criticism about his lack of experience in Washington might be taking a toll.
Mr Obama says he's putting his faith in the people of Iowa
"That may have some effect, but ultimately I'm putting my faith in the people of Iowa and the people of America that they want something better," he said.
Mrs Clinton, on the other hand, played on her experience, telling This Week that she had once been "intimately involved in so much that went on in the White House, here at home and around the world".
Candidates who do well in Iowa and New Hampshire can gain momentum and media attention, establishing themselves as front-runners.