Madonna, performing at the premier of her Sticky and Sweet tour at Cardiff's Millennium Stadium in Wales on Saturday, is again courting controversy. (Joel Ryan/Associated Press)

Campaign officials for U.S. Senator and Republican presidential candidate John McCain have shot back at Madonna for a segment of her just-launched new concert tour.

Madonna kicked off her Sticky and Sweet world tour at Millennium Stadium in Cardiff, Wales, on Saturday. During her performance of Get Stupid, an image of McCain is shown alongside those of Adolf Hitler and Robert Mugabe, as well as photos of global warming and destruction.

Later in the concert, Democratic presidential candidate Barack Obama's face is shown in a sequence that also includes images of Mahatma Gandhi, John Lennon and Al Gore.

"The comparisons are outrageous, unacceptable and crudely divisive all at the same time," said Tucker Bounds, a McCain campaign spokesman.

"It clearly shows that when it comes to supporting Barack Obama, his fellow worldwide celebrities refuse to consider any smear or attack off limits."

Earlier this month, the McCain campaign released a television ad portraying Obama as a celebrity, juxtaposing images of the Illinois senator with photos of Britney Spears and Paris Hilton. Shortly after, hotel heiress and notorious party-girl Hilton starred in a tongue-in-cheek internet rejoinder that poked fun at the "wrinkly, white-haired dude" who endorsed her for president with his ad.

Madonna regularly courts controversy

No stranger to controversy, Madonna has regularly sparked protests throughout her career.

A frequent critic has been the Roman Catholic Church, which along with Jewish and Muslim leaders, objected to a mock crucifixion scene she staged during 2006's Confessions tour.

In 1990, Toronto police threatened to arrest her for simulating masturbation on stage as part of a concert for her Blond Ambition tour.

About three years later, during a concert in Puerto Rico for her Girlie Show world tour, Madonna reportedly angered officials by rubbing the Puerto Rican flag between her legs.

She has also been criticized for her music videos, including Like a Prayer, which features burning crosses, religious statues crying blood and Madonna seducing an actor portraying a black saint, and Justify My Love, which has scenes of sadomasochism, bondage, same-sex kissing and brief nudity.