Front-runner Mitt Romney has won victories in primary elections in the states of Michigan and Arizona in the contest to become the U.S. Republican Party's nominee to face President Barack Obama in November's U.S. election.
With almost all votes counted from the February 28 balloting in Michigan, Romney won 41 percent, while his main rival, Rick Santorum, had 38 percent.
Analysts say Romney's failure to achieve a dominating victory in Michigan -- a state where he grew up and his father once served as governor -- means the contest to become the Republican nominee is not yet decided.
After learning he had won the Michigan primary, Romney noted it had been a close race.
"We didn't win by a lot, but we won by enough and that's all that counts," he said.
Romney, a former Massachusetts governor, had at one point been seen as the almost-certain nominee of the Republicans -- but Santorum's challenge strengthened after winning contests in Colorado, Minnesota, and Missouri earlier this month.
Santorum acknowledged his narrow defeat but thanked his voters for his better-than-expected result.
"I am so thankful, so thankful, to so many people here tonight," he said. "First and foremost, I just have to say to the people of Michigan, you know, we came into the backyard of one of my opponents in a race that everyone said, 'Well, just ignore it, you have really no chance here.' And the people of Michigan looked into the hearts of the candidates and all I have to say is, 'I love you back.'"
In the southwestern state of Arizona, Romney easily won, with 47 percent of the vote to Santorum's 27 percent, with 93 percent of the vote counted.
Two other candidates, former speaker of the House of Represenatives Newt Gingrich and Texas congressman Ron Paul also took part in the February 28 contests.
Gingrich, who was once seen as a potential front-runner for the Republican nomination, won 16 percent in Arizona and 7 percent in Michigan, while Paul obtained 12 percent in Michigan and 8 percent in Arizona.
On March 6, the so-called "Super Tuesday" primaries will be held in 10 states with a total of 419 delegates up for grabs. That's more than one-third of the delegates needed to secure the nomination at the Republican National Convention in August, where the nominee will be formally chosen.
A candidate needs 1,144 delegates to win the nomination. Romney so far has 152 delegates, while Santorum has gathered 72. Gingrich comes third with 32, and Ron Paul is fourth, with 19.
Based on reporting by AP, Reuters, AFP, and dpa