U.S. President Barack Obama said Friday that he was surprised to learn that he won the Nobel Peace Prize of 2009, which he saw as a "call for action."

U.S. President Barack Obama delivers a speech after he received the 2009 Nobel Peace Prize in Rose Garden of White House in Washington on Oct. 9, 2009. [Zhang Yan/Xinhua]

Speaking to reporters in the Rose Garden of the White House, he said he was "both surprised and deeply humbled" to accept the award and didn't view it as a recognition of his own accomplishments.

Rather, the prize should be regarded as a recognition of the goals he set for the United States and the world.

"I will accept this award as a call to action, a call for all nations to confront the common challenges of the 21st century," Obama said.

The president said the challenges, including nuclear nonproliferation, combating climate change and energy crisis, can't be met by any one leader or any one nation.

"That is why I worked to establish a new era of engagement in which all nations must take responsibility for the world we seek," he said.

Earlier Friday, the Norwegian Nobel Committee announced Obama was awarded the 2009 Nobel Peace Prize for "his extraordinary efforts to strengthen international diplomacy and cooperation between people."

U.S. President Barack Obama delivers a speech after he received the 2009 Nobel Peace Prize in Rose Garden of White House in Washington on Oct. 9, 2009. [Zhang Yan/Xinhua]

Obama is the fourth U.S. president to win the Nobel Peace Prize and the third sitting president to do so.

Reactions to his winning of the Nobel Peace Prize are mixed in the United States.

Some like former U.S. President Jimmy Carter, the Nobel Peace Prize winner of 2002, said Obama's award is "a bold statement of international support for his vision and commitment to peace and harmony in international relations."

Others, like the Time Magazine's Mark Halperin, said "the stunning decision to award Obama the Nobel Peace Prize for his rhetoric will almost certainly infuriate his detractors in America more than it will delight his supporters."