Rick Santorum has widened his lead over Mitt Romney in the race for the U.S. Republican presidential nomination, according to a new Gallup national poll released on Monday.

Thirty-six percent of Republican voters and Republican-leaning independents back Santorum, the former U.S. senator from Pennsylvania, to become the party's nominee, eight points ahead of Romney, the former Massachusetts governor who is at 28 percent, according to Gallup's daily tracking of the GOP ballot support.

Former House speaker Newt Gingrich came in third at 13 percent, with U.S. Representative from Texas Ron Paul at 11 percent.

Riding strong performances in GOP caucuses in Colorado and Minnesota and a non-binding primary in Missouri on Feb. 7, Santorum has seen his poll numbers skyrocketing to atop the field both nationally and in some key battlegrounds.

The former senator surged to tie Romney a week ago in Gallup national surveys, and has since been able to widen his lead over the long-time GOP front-runner.

In the upcoming pivotal GOP presidential contest in Michigan, which was supposed to be Romney's stronghold as he was born there and his father had been a popular governor of the state, Santorum also has edge over Romney, though the margin has somewhat narrowed in recent days.

The latest survey from Public Policy Polling showed Santorum leading with 37 percent support of likely Republican voters in Michigan, which holds primary on Feb. 28, ahead of Romney with 33 percent. The 4-point lead has narrowed down from 15 points in the same poll last week.

Romney's staunch opposition to government bailout of the auto industry could have hurt him in Michigan, home to the U.S. auto giants, analysts said.