President Barack Obama spoke to an enthusiastic audience of admiring Czechs and fawning US nationals Sunday morning in Prague, assuring the world that the US intends to lead the effort to rid the world of nuclear weapons.

The timing of the speech was notable, given that North Korea on Sunday launched a long-range rocket over the Pacific, defying appeals from the international community to back off its earlier announced launch plans. Obama described the North Korean rocket launch on Sunday as a provocative act, and urged Pyongyang to refrain from further provocative actions.

Perched high above the city at the foot of Prague Castle, Obama pledged to pursue the peace and security of a world without nuclear weapons.

This goal will not be reached quickly - perhaps not in my lifetime, said the President. It will take patience and persistence. But now we, too, must ignore the voices who tell us that the world cannot change.

As the only nuclear power to have used a nuclear weapon, the United States has a moral responsibility to act. We cannot succeed in this endeavor alone, but we can lead it, promised Obama.

Obama also promised to negotiate a new strategic arms reduction treaty with Russia this year.

President Medvedev and I began this process in London, and will seek a new agreement by the end of this year that is legally binding, and sufficiently bold, insisted the President.

Obama also said his administration will immediately and aggressively pursue U.S. ratification of the Comprehensive Test Ban Treaty.

After more than five decades of talks, it is time for the testing of nuclear weapons to finally be banned, he said to a crowd estimated at nearly 40,000.

While issues of defence have taken a back seat of late due the global economic crisis, Obama used Sunday's North Korean launch to remind the world why we need a new and more rigorous approach to address this threat.

Now is the time for a strong international response, thundered Obama. North Korea must know that the path to security and respect will never come through threats and illegal weapons. And all nations must come together to build a stronger, global regime.

Turning to Iran, the President expressed support for Iran's right to peaceful nuclear energy with rigorous inspections, but insisted that Iran's nuclear and ballistic missile activity poses a real threat, not just to the United States, but to Iran's neighbors and US allies in the Middle East.

This week, Obama has made a whirlwind tour of Europe, starting at in the UK for the G-20, where global leaders promised renewed spending and increased regulation in hopes of bringing about a soft landing for world economy.

Moving onto Strasbourg, Obama met with NATO officials, praising its allies for support in the US effort in Afghanistan, welcoming promised down payment of 5,000 new forces.

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