Barack Obama has outlined his vision of a world free of nuclear weapons in a major speech in Europe.
The US president called for a global summit on nuclear security and the forging of new partnerships to prevent the spread of nuclear weapons.
He said he hoped to negotiate a new treaty to end the production of fissile materials for nuclear weapons.
North Korea's "provocative" rocket launch earlier in the day underscored the need for action, he said.
Although his nuclear goals might not be realised in his lifetime, he said he would strive to achieve them.
Mr Obama said that as long as Iran continued to pose a potential nuclear threat, the US would continue to work on a controversial missile defence shield, parts of which would be stationed in Poland and the Czech Republic.
He was speaking ahead of a meeting with EU leaders in the Czech capital, Prague, hours after North Korea launched a rocket despite international warnings.
Mr Obama condemned the launch: "Now is the time for a strong international response," he said.
"North Korea must know that the path to security and respect will never come through threats and illegal weapons."
