PRAGUE, CZECH REPUBLIC, AND WASHINGTON — President Obama vowed Sunday to pursue the elimination of nuclear weapons from the planet, telling a cheering throng in Prague that the United States is ready to lead an international effort to reduce atomic arsenals and the threat they pose.
Speaking only hours after North Korea launched a multistage rocket, drawing new international concern and condemnation, Obama outlined a plan to work toward a goal that he acknowledged remains decades away.
"As the only nuclear power to have used a nuclear weapon, the United States has a moral responsibility to act," Obama told a crowd of more than 20,000 in Prague's historic Hradcany Square. "We cannot succeed in this endeavor alone, but we can lead it."
His speech in Eastern Europe in front of the spires of a medieval castle came as Eastern Europeans mark the 20th anniversary of the fall of communism, ending the Cold War that for decades defined American relations with the world.
"The existence of thousands of nuclear weapons is the most dangerous legacy of the Cold War," Obama told the crowd. "Today, the Cold War has disappeared, but thousands of those weapons have not."
On his first tour of Europe as president, Obama then laid out a process to stop the spread of nuclear weapons, ban nuclear testing, and secure loose fissile material from terrorists. Until weapons and the material to make them are fully secured, Obama said, the U.S. would maintain its nuclear arsenal to deter adversaries.
Noting the North Korean rocket launch, which many in the West fear was a test of the regime's ability to deliver a nuclear warhead, the president called for that country's leaders and Iran to join in halting the spread of weapons of mass destruction.
"North Korea must know that the path to security and respect will never come through threats and illegal weapons," Obama said. He added that his administration would engage diplomatically with Iran, another nation pursuing nuclear technology, based on "mutual interests and mutual respect."
"We will support Iran's right to peaceful nuclear energy with rigorous inspections. That's a path that the Islamic Republic can take," he said. "Or the government can choose increased isolation, international pressure, and a potential nuclear arms race in the region that will increase insecurity for all."
If Iran remains a risk, Obama said, he would favor going forward with a controversial missile defense system that would be based in the Czech Republic and Poland. Russia and peace activists in Prague oppose the system.
"If the Iranian threat is eliminated, we will have a stronger basis for security, and the driving force for missile defense construction in Europe will be removed," Obama said.
In the outdoor speech, Obama promised to negotiate a strategic arms reduction treaty with Russia by the end of the year that will significantly reduce the number of nuclear warheads. A few days earlier, Obama and Russian President Dmitry Medvedev agreed during meetings in London to produce a new arms control treaty to replace the current Strategic Arms Reduction Treaty, known as START, that expires in December.
The president also called for strengthening the Nuclear Nonproliferation Treaty, meant to allow access to nuclear power for nonmilitary use and to secure nuclear weapons and ingredients from terrorists.
His plan also called for peaceful uses of nuclear power using an international fuel bank that would be available to every nation that renounces nuclear weapons. He said he supports Iran's right to pursue nuclear energy, providing the regime agrees to regular and thorough inspections. Finally, Obama said he hoped to host a world summit on nuclear weapons within the year.
Obama's speech received mainly positive reactions from interest groups and arms control advocates.
"The president is absolutely correct that our long-term goal must be a world free from nuclear weapons," said Sen. John F. Kerry (D-Mass.), chairman of the Senate Foreign Relations Committee, applauding Obama's proposal to host a Global Summit on Nuclear Security.
Former Republican Sen. Chuck Hagel of Nebraska called on leaders of nuclear nations to back the "bold and historic effort" by Obama and Medvedev to reduce weapons.
One activist group expressed regret that Obama was not more forceful.
"President Obama's statement that such a world might not be achieved in his lifetime is very disappointing," said Kevin Martin, executive director of Peace Action, an anti-nuclear organization.
North Korea's rocket launch gave added urgency to Obama's long-planned speech. The president said he thinks it is a clear violation of the resolutions of the U.N. Security Council. North Korea, the president said, faces a decision much like Iran's, as the U.S. and allies attempt to stem nuclear weapons for both.
"If they want to take an appropriate path to rejoin the international community and break out of their isolation, that's available to them," Obama said of North Korea.