By Ross Colvin and Wojciech Moskwa
OSLO (Reuters) - President Barack Obama defended the right of the United States to wage "just wars" as he accepted the Nobel Peace Prize on Thursday, acknowledging that as a wartime president he was a controversial choice.
In a speech at the award ceremony in Oslo, preceded by a fanfare of trumpets, Obama declared he would not "stand idle" in the face of threats to the United States.
He raised the specter of a new nuclear arms race, potentially in the Middle East or East Asia, and called for tough sanctions against nations that did not abide by international laws, a warning to Iran and North Korea.
Obama also acknowledged criticism that he does not deserve the prize and has few tangible gains to show from his nearly 11 months in office, saying he was "at the beginning, and not the end, of my labors on the world stage."
The president's acceptance speech, punctuated with references to past winners of the peace prize, was notable for its dominant theme of war.
He was speaking just nine days after ordering 30,000 more U.S. troops to Afghanistan in a major expansion of the eight-year-old war. Obama hopes the additional troops will help to break the momentum of a resurgent Taliban and buy time to train Afghan security forces to take over from the Americans.
In his only reference to the troop build-up, Obama said: "We are at war, and I am responsible for the deployment of thousands of young Americans to battle in a distant land. Some will kill. Some will be killed. "
Obama walked a rhetorical tightrope in addressing the paradox of a president receiving the highest award for peace while waging two major foreign conflicts, in Iraq and Afghanistan.
"Perhaps the most profound issue surrounding my receipt of this prize is the fact that I am the commander-in-chief of a nation in the midst of two wars," he said.
"There will be times when nations -- acting individually or in concert -- will find the use of force not only necessary but morally justified," he said, adding that the Afghanistan war had been forced on the United States by the September 11, 2001, attacks, which were masterminded by al Qaeda from there.
He said he was mindful of civil rights leader and Nobel peace laureate Martin Luther King's statement that "violence never brings permanent peace."
But, Obama said, "I face the world as it is, and cannot stand idle in the face of threats to the American people."
There was loud applause from some 900 invited guests as Obama accepted the award in a grand room in Oslo's city hall, becoming the third sitting U.S. president to receive the Nobel peace prize in its 108-year history.
While the award has excited international interest, Americans are preoccupied with double-digit unemployment and are more concerned about how Obama plans to generate new jobs. Americans remain anxious about the economy, nudging Obama's approval ratings to 50 percent or below.
Obama said the United States must uphold moral standards when waging wars that were necessary and justified.
"Even as we confront a vicious adversary that abides by no rules, I believe that the United States of America must remain a standard bearer in the conduct of war. That is what makes us different from those whom we fight," he said.
By pledging to close the Guantanamo Bay prison for foreign terrorism suspects on Cuba and outlawing harsh interrogation techniques, Obama has attempted to recover the moral high ground that critics accused his predecessor George W. Bush of surrendering by waging a no-holds-barred war on terrorism.
In seeking alternatives to force, it was necessary to be tough, Obama said.
"Those regimes that break the rules must be held accountable. Sanctions must enact a real price," Obama said in a passage that addressed North Korea's nuclear arsenal and U.S. suspicions that Iran, too, seeks to acquire the bomb.
"Those who seek peace cannot stand idly by as nations arm themselves for nuclear war."
On a rainy day with temperatures just above freezing, thousands lined heavily guarded Oslo streets to greet Obama.
Supporters heavily outnumbered the critics, one of whose banners read: "Obama you won it, now earn it."