U.S. President Barack Obama has warned North Korea against launching what the United States believes to be a missile.

At a news conference in the French city of Strasbourg, Obama said that if North Korea decides to launch a rocket, the United States will work with all interested parties in the international community to take appropriate steps to let North Korea know that it can't threaten the safety and security of other countries with impunity.

He said his administration has "made it very clear to the North Koreans that their missile launch is provocative."

Later in the day, Obama met young Europeans in a town-hall style gathering.

He pointed out that reducing the threat of nuclear proliferation will be difficult without serious steps taken by nuclear powers, including the United States and Russia, to reduce their own nuclear arsenals.

He said that only then will they have the moral authority to dissuade North Korea and Iran from developing or proliferating nuclear weapons.