Former Massachusetts governor Mitt Romney has narrowly won the first vote by Republican party supporters in the United States for their preferred presidential candidate.
Seven Republican candidates were vying to challenge Barack Obama for the White House in November this year.
Mr Romney beat his closest rival former senator Rick Santorum by just eight votes out of 122,255 votes cast in the state of Iowa, the BBC reports. Both men had 25% support.
Mr Romney said he had run a national campaign, whereas Mr Santorum had focused his effort entirely on Iowa, and he planned to win the Republican nomination to stand against Mr Obama.
Ron Paul was third and Newt Gingrich fourth.
Texas Governor Rick Perry says he is staying in the race, despite finishing fifth, while sixth-placed Michele Bachmann has ended her campaign.
Further caucuses and primary elections will be held in all 50 states, Washington DC and other territories over the next few months. The next vote is in New Hampshire.
The eventual nominee will be formally anointed at the Republican National Convention in Florida in August.