WASHINGTON (CNN) -- Former Massachusetts Gov. Mitt Romney has opened up a 12 point lead in Iowa, according to a Des Moines Register poll released Monday.

Romney is the first choice of 30 percent of likely Republican Iowa caucus goers, while Arizona Sen. John McCain and former New York City Mayor Rudy Giuliani are locked in a virtual tie for second place, 18 percent to 17 percent respectively. The remaining GOP candidates were in single digits.

On the Democratic side, former North Carolina Sen. John Edwards leads the pack in the battle for his party's nomination, registering 29 percent in the poll -- six percentage points higher than Illinois Sen. Barack Obama. New York Sen. Hillary Clinton is a close third at 21 percent and New Mexico Gov. Bill Richardson, who officially launches his presidential bid Monday, registers 10 percent. The remaining candidates polled in single digits.

The poll, which surveyed 401 likely Republican caucus goers and 400 likely Democratic caucus goers, was conducted on May 12-16 and carries a margin of error of plus or minus 4.9 percentage points.