American superstars Oprah Winfrey and Tom Cruise said Saturday that hosting this year's Nobel Peace Prize Concert in front of up to 450 million viewers was both an honor and a way to contribute to the struggle for peace.

Winfrey and Cruise were to co-host Saturday's concert in Oslo, held to honor Kenyan environmentalist Wangari Maathai. The concert will also feature musical artists such as British teen soul singer Joss Stone, opera vocalist Andrea Bocelli , jazz singer Diana Krall, and pop singers Cyndi Lauper and Patti Labelle.

Winfrey said she didn't have to think twice before accepting the offer to host the concert, which was to be broadcast live in more than 100 countries.

"I'm here because, first of all, when the Nobel Committee calls, you try to answer with a yes," the talk show host told reporters before the show. Plus, she added, "I like to go wherever Tom Cruise might be."

"You have the Nobel Committee and Tom Cruise — who's gonna say no to that?" she said.

Cruise said that his religion, Scientology, was part of the reason he felt strongly about the award.

"One of the things that we believe in (as Scientologists) is peace, freedom," the movie actor said. "I'm just proud to be here, and very proud to be a Scientologist here and to be part of this."

The 64-year-old Maathai, Kenya's deputy environment minister, was honored as founder of the Green Belt Movement, which has sought to empower women, improve the environment — by planting 30 million trees — and fight corruption in Africa for almost 30 years.

Winfrey and Cruise both lauded the choice of Maathai, the first environmentalist and first African woman to be awarded the coveted peace prize.

"What a momentous occasion this is for not just African women, but particularly for African girls," Winfrey said. "In Maathai, African girls have a role model they can look at and say, 'I want to be like her,'" Winfrey said.

In the United States, the concert was to be broadcast on Dec. 23 by E! Entertainment Television.