Republican presidential front-runner Donald Trump is maintaining a solid lead in the race to become the party's standard-bearer, one week ahead of the first vote in Iowa, voter surveys showed Tuesday.

An ABC-Washington Post poll put Trump atop the race with 37 percent of support from Republican-leaning voters, followed by Se.

Ted Cruz (R-TX) with 21 percent, Sen. Marco Rubio (R-FL) with 11 percent and Ben Carson with 7 percent.

Moreover, 64 percent of Republican-leaning voters, regardless of which candidates they support, predicted that Trump is most likely to win the Republican presidential nomination, well ahead of 12 percent of voters who thought Cruz would emerge victorious.

The phone survey of 1,001 adults was conducted Jan. 21-24 and had a margin of error of plus or minus 5.5 percentage points. Of the total respondents, 356 were Republican-leading registered voters.

A CNN-Opinion Research Corporation (ORC) survey of 405 Republicans and Republican-leading voters also put Trump atop the race with a record 41 percent of support, more than twice Cruz's 19 percent. Rubio received 8 percent of support and Carson 6 percent.

The Jan. 21-24 survey had a margin of error of plus or minus 5 percentage points.

CNN said it was the first time Trump has topped the 40 percent mark in CNN/ORC polling.

In Iowa, where the first votes of the Republican presidential race will be cast on Monday, however, Trump and Cruz are in a dead-heat contest, with 31 percent and 29 percent of support, respectively, according to a statewide poll by Quinnipiac University.

The difference between the two front-runners is within the poll's margin of error of plus or minus 3.8 percentage points.

Quinnipiac University surveyed 651 Iowa likely Republican Caucus participants from Jan. 18 to 24.

The result is virtually unchanged from results of a Jan. 11 survey by Quinnipiac University showing Trump at 31 percent, with 29 percent for Cruz and 15 percent for Rubio, according to the Des Moines Register, a newspaper in Iowa.

"One week before the caucuses gather, the question is which candidate has the best field organization. If the events of the last two weeks haven't moved the needle, one wonders what would change it in the next six days," Peter A. Brown, assistant director of the Quinnipiac University Poll, was quoted as telling the newspaper.

Trump has been leading the Republican presidential nomination race as he made a series of unbridled remarks and sensational proposals on immigration and other sensitive issues that apparently struck a chord with conservatives.

The billionaire real-estate mogul has a biased view on South Korea, and has repeated unfounded accusations that the wealthy Asian ally pays almost nothing when the U.S. provides it with protection from North Korean threats.

South Korea has long shouldered part of the burden needed for the upkeep of 28,500 American troops stationed in the country. In 2014, the two countries renewed their cost-sharing agreement, known as the Special Measures Agreement, with Seoul agreeing to pay 920 billion won ($886 million) for the upkeep of the U.S. troops per year, a 5.8 percent increase. (Yonhap)