Republican Party officials said former governor of Massachusetts Mitt Romney beat Rick Santorum, former senator of Pennsylvania, in the Iowa caucuses by just eight votes.

The two candidates were in a dead heat for most of Tuesday night until the Iowa Republican Party declared Romney the winner. According to the Associated Press, both candidates had a 25 percent share of the ballots, with Romney securing 30,015 votes and Santorum 30,007. There were about 122,000 votes cast in the race.

Representative Ron Paul placed a strong third with 21 percent, while former US House Speaker Newt Gingrich, who was riding high in the polls less than a month ago, ended fourth with 13 percent.

Texas governor Rick Perry scored 10 percent and congresswoman Michele Bachmann attracted 5 percent. Perry announced he was returning to Texas to reassess his presidential bid.

"With the voters' decision tonight in Iowa, I have decided to return to Texas to assess the results of tonight's caucus and determine whether there's a path forward in this race," he told supporters. "With a little prayer and reflection I'm going to choose the best path forward."

In an email to supporters, Santorum wrote: "We shocked the world last night in Iowa. We did it with a coalition of conservatives, Tea Party members and values voters who recognised that my successful conservative record gives the GOP the best chance to defeat Barack Obama."