U.S. Republican presidential contender Mitt Romney has attacked rival Rick Santorum as a political insider prone to big government spending.

Santorum, a former Pennsylvania senator, is in a battle with Romney for frontrunner status in the bid for the Republican presidential nomination. The nominee will take on President Barack Obama, A Democrat, in November's general election. Romney is a former governor of Massachusetts.

Speaking at an event Thursday in Arizona — one of two states holding primaries next week — Romney said his team is “the American people,” not the “insiders in Washington.”

The two men are running neck-in-neck in Michigan — the other state with a primary next Tuesday. Last week, some polls showed Santorum with a significant lead there.

In Arizona, polls show Romney ahead of Santorum. However, in polling nationwide, Santorum continues to have a clear lead, with nearly 34 percent support over Romney's 28 percent.

Fellow contenders Newt Gingrich, a former House of Representatives speaker, and Ron Paul, a Texas congressman, trail far behind.

A week after the primaries in Arizona and Michigan , voters in an additional 10 states head to the polls in what is known as “Super Tuesday.”