Iowa caucus: Mitt Romney and Ron Paul nearly neck and neck
Republican presidential candidate Mitt Romney maintains a slim lead over his rival, Ron Paul, days before the Iowa caucus, according to the latest poll.
Rick Santorum's surge continues - he is third - while Rick Perry has inched up to fourth and Newt Gingrich has slipped to fifth. Michele Bachmann was last.
Meanwhile, Mr Gingrich wept at an Iowa campaign event as he discussed his mother's battle with bipolar disease.
The candidates are making their final pitch to voters ahead of Iowa's vote.
The Hawkeye state's 3 January gathering marks the start of the six-month period during which each US state will hold primary elections or caucuses to pick a Republican candidate, who will be officially nominated at the party convention in August.Romney tax returns
Friday's NBC/Marist poll from Iowa put Mr Romney in the lead on 23%, with Mr Paul on 21%, Mr Santorum on 15%, Mr Perry on 14% and Mr Gingrich on 13%.
Buoyed by the third survey in as many days placing him as the Iowa front-runner, former Massachusetts Governor Romney is making an all-out bid to win the state's caucus.
He had barely campaigned in the state since its caucus-goers helped derail his last run for the presidency four years ago.
Correspondents say the moderate Republican has been helped by social conservatives' inability to decide between Mr Perry, Mrs Bachmann and Mr Santorum.
Campaigning in the town of Des Moines on Friday, Mr Romney sought to portray the libertarian-leaning Mr Paul as an unelectable fringe candidate.
While Mr Paul enjoys support in Iowa, the new poll also suggested 41% of people in the state thought he was an "unacceptable" candidate.
Mr Romney also said Democratic President Barack Obama had tried to convince American voters the nation's economy could be worse.
"That goes down with Marie Antoinette, 'let them eat cake'," he said, referring to remarks reputedly made by the Austrian-born French queen who was beheaded during France's revolution.
But the former governor himself faced accusations of being out of touch with voters as the Democratic National Committee released an internet video, What is Mitt Romney Hiding?, challenging the multimillionaire to release his income tax returns.
Mr Romney refused again on Friday to reveal how much tax he pays, saying: "If I become president, why, then I can decide that."Gingrich weeps
Mr Gingrich revealed a softer side on Friday as he cried during an event with a group of mothers in an Iowa coffee shop, when asked to recall a moment that changed his life.
The former House Speaker, who has fallen from the top of the polls in a hail of attack ads, started to describe his mother's struggle with depression, when the tears began to flow.
Mr Santorum, a former Pennsylvania senator, has suddenly surged this week after spending most of the last few months in the lower tier of candidates.
Correspondents say Texas Governor Perry's poll rise in Iowa may be down to support from the state's evangelical voters.
This week he moved further right on abortion, advocating a total ban on the procedure, including in cases of rape and incest.
Minnesota Congresswoman Bachmann, meanwhile, has been trying to convince backers her campaign is not in meltdown after a top Iowa supporter defected to Mr Paul.
The Tea Party heroine compared herself to Margaret Thatcher, Britain's first female prime minister, at a campaign event on Thursday, saying she wanted to be "America's Iron Lady".
The eventual Republican candidate will challenge Barack Obama for the White House in November 2012.
Many voters are concerned by the pace of economic recovery from the recession that started during the end of the presidency of George W Bush and ended in 2009.