US President Barack Obama Thursday accepted the 2009 Nobel Peace Prize with deep gratitude and “humility” but warned that war was sometimes necessary despite its “acute” human tragedy. “I receive this honor with deep gratitude and great humility,” Obama said in an elaborate ceremony enshrining him as a Nobel laureate here. “It is an award that speaks to our highest aspirations - that for all the cruelty and hardship of our world, we are not mere prisoners of fate. “Our actions matter, and can bend history in the direction of justice,” Obama said at the Oslo City Hall. Obama admitted there had been criticism of his award, and accepted he did not belong in the same company as previous laureates like Martin Luther King and Nelson Mandela. He also took on the irony that he was accepting a peace prize just after deciding to escalate the war in Afghanistan with 30,000 more US troops. “The instruments of war do have a role to play in preserving the peace,” Obama said. “And yet this truth must coexist with another - that no matter how justified, war promises human tragedy. “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.” Obama also argued that when force was necessary, the United States “must remain a standard bearer in the conduct of war.” OSLO - The United States must uphold moral standards when waging wars that are necessary and justified, US President Barack Obama said Thursday as he accepted the Nobel Prize for Peace. In a speech at the award ceremony in Oslo, Obama said violent conflict would not be eradicated “in our lifetimes,” there would be times when nations would need to fight just wars and he would not stand idle in the face of threats to the American people. “Where force is necessary, we have a moral and strategic interest in binding ourselves to certain rules of conduct. And even as we confront a vicious adversary that abides by no rules, I believe that the USA must remain a standard bearer in the conduct of war,” he declared. Obama acknowledged the criticism of those who have said it was wrong and premature to award the Nobel accolade to a president still in his first year in office and escalating a major war. He said America's adherence to moral standards, even in war, was what made it different from its enemies. “That is a source of our strength. That is why I prohibited torture. That is why I ordered the prison at Guantanamo Bay closed. And that is why I have reaffirmed America's commitment to abide by the Geneva Conventions,” he said. Acknowledging “a reflexive suspicion of America, the world's sole military superpower,” he said his country could not act alone in confronting global challenges. “Those regimes that break the rules must be held accountable. Sanctions must enact a real price.” “It is...incumbent upon all of us to insist that nations like Iran and North Korea do not game the system,” Obama said. At a news conference earlier, Obama reaffirmed that US troops would begin transferring responsibility for Afghan security to local forces in July 2011 but said there would be no “precipitous drawdown.” On a rainy day, thousands lined heavily guarded Oslo streets to greet Obama. Only handfuls of protesters were visible, with one group holding a sign reading: “Obama you won it, now earn it.” Environmentalists in the crowd called on the US leader to sign an ambitious deal to fight global warming when he visits nearby Copenhagen next week for the climax of a UN climate conference involving nearly 200 countries. Obama also paid tribute to anti-government demonstrators in Iran. Obama's Nobel snubs ‘impolite' A majority of Norwegians consider “impolite” US President Barack Obama's decision to snub parts of the official Nobel Peace Prize programme in Oslo this week, a poll showed. According to a poll conducted by the InFact institute and published in daily Verdens Gang (VG), 44 percent of 1,000 people surveyed said it was “impolite” of Obama to not lunch with the king, while 34 percent said it was okay. More than half, 53 percent, said it was “impolite” not to attend the Nobel concert, while 27 percent disagreed.