U.S. President Barack Obama called for the elimination of nuclear weapons on Sunday, calling them "the most dangerous legacy of the Cold War" during a speech given just hours after North Korea launched a rocket in defiance of international requests not to do so.

Obama said his government would "immediately and aggressively" seek a ban on the testing of nuclear weapons.

"Some argue that the spread of these weapons cannot be checked -- that we are destined to live in a world where more nations and more people possess the ultimate tools of destruction," Obama said to a crowd of more than 20,000 outside the Prague Castle gates.

"This fatalism is a deadly adversary," he said. "For if we believe that the spread of nuclear weapons is inevitable, then we are admitting to ourselves that the use of nuclear weapons is inevitable."

Obama indicated that the United States would host a summit within the next year that would include discussions to reduce and eventually eliminate nuclear weapons.

He also sharply rebuked North Korea for launching the rocket, which the international community believes was a test of the country's long-range missile technology.

The U.S., Japan and other countries believe that the North Koreans could use a missile in the future to carry a nuclear warhead.

"North Korea broke the rules once more by testing a rocket that could be used for a long range missile," Obama said. "This provocation underscores the need for action -- not just this afternoon at the UN Security Council, but in our determination to prevent the spread of these weapons."

During a meeting with European Union leaders later in the day, Obama called for a joint statement condemning the North Korean move. That statement is expected at some point on Sunday.

"North Korea's development of a ballistic missile capability, regardless of the stated purpose of this launch, is aimed at providing it with the ability to threaten countries near and far with weapons of mass destruction," a joint EU-U.S. statement said.

Obama backs Turkey's inclusion in EU

Obama also urged the European Union to welcome Turkey as a full member of the 27 nation bloc.

"Moving forward toward Turkish membership in the EU would be an important signal of your (EU) commitment to this agenda and ensure that we continue to anchor Turkey firmly in Europe," he told EU leaders.

Turkey has long been seeking to join the bloc, and Obama's comments were a reaffirmation of U.S. support for that goal.

Following his meeting with EU leaders, Obama flew to Turkey; the final stop in his inaugural trip oversees.

The American leader's two day visit to Turkey -- the only Muslim member nation of NATO -- is intended to strengthen ties between the two allies. Obama will address the Turkish parliament and visit the mausoleum of the founder of modern Turkey, Mustafa Kemal Ataturk. He'll also do some sightseeing.

The visit, which is Obama's first to a Muslim country, is seen as symbolic in terms of unity and strategy, as the new administration tries to improve the U.S.' tarnished image abroad.

With files from The Associated Press