OSLO (AFP) US President Barack Obama on Thursday accepted the Nobel Peace Prize, uncomfortably acknowledging his role as a leader at war while insisting that conflict can be morally justified. Obamas elevation to a pantheon of winners alongside the likes of Nelson Mandela, Mother Teresa and Martin Luther King before he has even spent a year in office has sparked international debate. Obama said he received the award with great humility. Compared to some of the giants of history who have received this prize - Schweitzer and King; Marshall and Mandela - my accomplishments are slight. The US president, who like other winners will get a diploma, a medal and 10 million krona (1.4 million dollars), dwelled at length on his responsibility fighting conflicts in Iraq and Afghanistan, where he has just sent 30,000 extra troops. War is sometimes necessary, and war is at some level an expression of human feelings. The United States has helped underwrite global security for more than six decades with the blood of our citizens and the strength of our arms, he said highlighting conflict in Europe and Asia. The service and sacrifice of our men and women in uniform has promoted peace and prosperity from Germany to Korea, and enabled democracy to take hold in places like the Balkans. Our actions matter, and can bend history in the direction of justice, Obama told the glittering event at Oslo City Hall, warning that diplomacy must be backed by consequences to beat repression. I am responsible for the deployment of thousands of young Americans to battle in a distant land. Some will kill. Some will be killed, he said. And so I come here with an acute sense of the cost of armed conflict - filled with difficult questions about the relationship between war and peace, and our effort to replace one with the other. Warning that was is never glorious, and we must never trumpet it as such, Obama argued that it could sometimes be not only necessary but morally justified, saying negotiations would not end the Al-Qaeda threat. The US leader paid tribute to anti-government demonstrators in Iran, Myanmar and Zimbabwe and said the United States would always stand on the side of those who sought freedom. We will bear witness to the quiet dignity of reformers like Aung Sang Suu Kyi; to the bravery of Zimbabweans who cast their ballots in the face of beatings; to the hundreds of thousands who have marched silently through the streets of Iran, Obama said. It is telling that the leaders of these governments fear the aspirations of their own people more than the power of any other nation. Obama has been closely questioned about his credentials since the Nobel committee made its shock announcement in October. Responding to the international controversy over the award, the chairman of the Norwegian Nobel Committee, Thorbjoern Jagland, told the prize ceremony that history can tell us a great deal about lost opportunities. It is now, today, that we have the opportunity to support President Obamas ideas. This years prize is indeed a call to action for all of us. Obama told a press conference before the ceremony that he would use the prize to bolster his pro-engagement foreign policy. The goal is not to win a popularity contest or to get an award, even one as prestigious as the Nobel peace prize. The goal has been to advance Americas interests, he said. If I am successful in those tasks, then hopefully some of the criticism will subside, but that is not really my concern. If I am not successful, then all the praise and the awards in the world wont disguise that fact. The Nobel committee praised Obama for nurturing a new era of engagement and multilateralism in US foreign policy when it made its shock announcement in October. Disappointment in Norway was mirrored in the United States, where the US leaders once huge popularity has started to fray and isolationist sentiment is on the rise. Several Norwegian peace and anti-nuclear organisations held demonstrations outside the award ceremony. Outside the Nobel committee offices, protestors held up a banner reading Obama you won the prize, now earn it. An InFact institute poll published Wednesday in the Verdens Gang daily showed just 35.9 percent of Norwegians thought Obama deserved the prize and 33.5 percent said he was unworthy. The medicine, physics, chemistry, economics and literature Nobel laureates will receive their awards at a ceremony in Stockholm on Thursday.