US President Barack Obama has formally accepted his Nobel Peace Prize during a ceremony in Oslo, Norway.

Obama acknowledged his critics who argued he had not done enough to deserve the prize. He also noted his decision to deploy another 30-thousand US troops to fight in Afghanistan. The president pointed out war was sometimes necessary and justified.

He said that people must accept "the hard truth" that violence cannot be eradicated and nations sometimes must wage war to protect their citizens from evil regimes or terrorism.

Obama was named the prize's recipient in October. The honor comes with a 1.4 million US dollar prize. The White House said Obama will donate the money to charities, but has not yet decided which ones.