The decision to award the Nobel Peace Prize to President Barack Obama stunned just about everyone - including the president.

Obama said he was "surprised and deeply humbled" by Friday's announcement. "To be honest," he said, "I do not feel that I deserve to be in the company of so many of the transformative figures who've been honored by this prize."

Many observers were shocked by the unexpected choice so early in the Obama presidency, which has yet to yield big achievements in peacemaking. However, Nobel officials said their pick was meant to build momentum behind Obama's initiatives to reduce nuclear arms, ease tensions with the Muslim world and stress diplomacy.

The prize announcement sparked almost instant and intense reactions on social networking sites such as Twitter and Facebook.

"Filled with happiness and hope by Obama's Nobel peace prize," wrote a tweeter from Australia.

But, a tweet from Germany declared, "Ridiculous! Barack Obama Wins Nobel Peace Prize. I am wondering what for? Replacing Bush? So far he has accomplished virtually nothing!"

Some reaction to the award was predictable, drawing liberal praise and conservative attacks.

House Speaker Nancy Pelosi (D-Calif.) said, "The Nobel Peace Prize is a testament to his leadership and vision and a tribute to American values."

Conservative radio talk-show Rush Limbaugh called the peace prize an "embarrassment," and said, "With this 'award' the elites of the world are urging Obama, the man of peace, to not do the surge in Afghanistan ..."

But, there were less predictable reactions.

Liberal filmmaker Michael Moore said, "The irony that you have been awarded this prize on the second day of the ninth year of what is quickly becoming your war in Afghanistan is not lost on anyone."

"I think all of us were surprised at the decision," said former GOP opponent John McCain, who once mocked Obama's celebrity. "But I think Americans are always pleased when their president is recognized by something on this order."

Past winner says: "I cannot think of anyone today more deserving of this honor. In less than a year in office, he has transformed the way we look at ourselves and the world we live in and rekindled hope for a world at peace with itself." - Mohamed Elbaradei, the director-general of the United Nations International Atomic Energy Agency, who received the Nobel Peace Prize in 2005.

Another winner says: "They say this is for his extraordinary efforts to strengthen international diplomacy and co-operation between peoples, and yet he continues the policy of militarism and occupation of Afghanistan, instead of dialogue and negotiation with all parties to the conflict." - Irish peace campaigner Mairead Corrigan Maguire, who received the Nobel Peace Prize in 1976.

Prize giver says: "Can someone tell me who did more than him this year? It is difficult to name a winner of the peace prize who is more in line with Alfred Nobel's will." - Thorbjoern Jagland, head of the Nobel Peace Prize committee and former Norwegian prime minister.