The president also declared that his far-reaching surveillance programs had saved lives on both sides of the Atlantic, as he sought to defend the controversial data-mining to skeptical Europeans.
Speaking against the soaring backdrop of the Brandenburg Gate, Obama said that "bold reductions" to the U.S. and Russian nuclear forces were needed to move the two powers away from the war posture that continues to seed mistrust between their governments.
"We may not live in fear of nuclear annihilation, but as long as nuclear weapons exist, we are not truly safe," Obama said as he closed a three-day visit to Europe, his first trip to the continent since winning re-election.
Obama is grappling with both domestic disputes and foreign policy challenges that have distracted from his second term agenda. Two matters — the fierce civil war in Syria and the U.S. government's domestic surveillance program — trailed Obama in Germany, as well as during the Group of 8 summit in Northern Ireland earlier this week.
Privacy-protective Germany was particularly eager for answers about the sweeping programs run by the National Security Agency. Chancellor Angela Merkel used a news conference with Obama Wednesday to appeal for "due diligence" in evaluating the privacy concerns, though she avoided a direct public confrontation with the president.
"There needs to be proportionality," she said of the U.S. programs. "This is going to be an ongoing battle."
Obama offered a lengthy defense of the court-approved surveillance of Internet and phone records, describing it as a targeted effort that has "saved lives."
"We know of at least 50 threats that have been averted because of this information, not just in the United States but in some cases threats here in Germany," he said.
The centerpiece of the president's visit was the afternoon speech at the Brandenburg Gate, where the Berlin Wall once stood, marking divisions between East and West Germany. Obama, standing behind a pane of bulletproof glass, spoke from the gate's East front, a location that would have been inaccessible to an American president in an earlier era.
The president's address drew inevitable comparisons to John F. Kennedy's famous "Ich bin ein Berliner" (I am a Berliner) speech exactly 50 years ago, as well as Obama's own thunderous welcome when he arrived in the city as a presidential candidate in 2008. More than 200,000 people filled the streets near Berlin's Victory Column for that address, a reflection of Europe's high hopes for the rising American political figure.
Now in his fifth year as president, Obama remains popular in Europe. But the crowd that gathered to hear him speak Wednesday was far smaller and less exuberant than it was in 2008 — just 4,500 people wilting in the sun on an unseasonably warm June day.
Obama took off his suit coat as he opened his remarks, telling the crowd, "We can be a little more informal among friends." Still, sweat beaded on his face as he read off a paper copy of his text because of problems with the teleprompter he normally relies on.
The wide-ranging address enumerated a litany of challenges facing the world, punctured by Obama's calls for the West to reignite the spirit that Berlin displayed as many citizens struggled to reunite the city during the Cold War.
"Today's threats are not as stark as they were half a century ago, but the struggle for freedom and security and human dignity, that struggle goes on," he said. "And I come here to this city of hope because the test of our time demands the same fighting spirit that defined Berlin a half-century ago."
The president commended Germany and other European nations for leading the way in tackling climate change, an issue he has pledged to make a priority in his second term. And he reiterated his desire to shut the Guantanamo Bay detention center, a comment that was enthusiastically received by the German crowd despite the president's failure to achieve the same goal during his first term.
Obama's nuclear pledges signaled an effort by the White House to revive a national security matter that has languished in recent years. But he set no deadlines for reaching a negotiated agreement with the Russians and his proposals were quickly questioned by officials in Moscow.
Russian foreign affairs official Alexei Pushkov told the Interfax news agency the proposals needed "serious revision so that they can be seen by the Russian side as serious and not as propaganda proposals." And Yuri Ushakov, foreign policy aide to President Vladimir Putin, told reporters that Moscow had already told the White House that any further arms reduction would have to involve countries besides just Russia and the United States.
"The situation is now far from what it was in the '60s and '70s, when only the USA and the Soviet Union discussed arms reduction," Ushakov said.
Obama also faced questions during his news conference with Merkel on deepening U.S. involvement in Syria and potential pitfalls in efforts to peacefully wind down the U.S.-led war in Afghanistan.
On Syria, Obama pointedly refused to detail steps his government has recently taken to arm rebels seeking to overthrow Syrian President Bashar Assad. U.S. officials have confirmed that the administration has approved weapons and ammunition shipments to the opposition.
"I cannot and will not comment on specifics around our programs related to the Syrian opposition," Obama said
The president also tried to explain away a surprise announcement that Afghan President Hamid Karzai was suspending talks with the U.S. on a new security deal in protest over the handling of initial peace negotiations with the Taliban. Obama announced the Taliban talks only one day prior, praising Karzai as he did as "courageous."
Obama said the U.S. had anticipated "there were going to be some areas of friction, to put it mildly, in getting this thing off the ground. That's not surprising. They've been fighting there for a long time" and mistrust is rampant. But he said it was important to pursue a parallel track toward reconciliation even as the fighting continued, and it would be up to the Afghan people as to whether that effort ultimately bore fruit.
First lady Michelle Obama and daughters Malia and Sasha traveled with Obama throughout his trip. The president and first lady were feted by the German government at a dinner Wednesday night before the family returned to Washington.
Associated Press writers Jim Kuhnhenn and Frank Jordans in Berlin and James Heintz in Moscow contributed to this report.
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Copyright 2013 The Associated Press.