President Barack Obama defended U.S. intelligence methods on a visit to Berlin on Wednesday, telling Chancellor Angela Merkel and wary Germans that Washington was not monitoring the emails of ordinary citizens or damaging civil liberties.

Obama is popular in Germany but revelations before the trip that the United States has a covert Internet surveillance program, codenamed Prism, have caused outrage in a country where memories of the eavesdropping East German Stasi secret police are still fresh.

Merkel said at a joint news conference that also touched on Afghanistan, Syria and the global economy, that the two leaders had held "long and intensive" talks on the spying issue, and pointed out that some questions still need to be cleared up.

"This is not a situation in which we are rifling through the ordinary emails of German citizens or American citizens or French citizens or anybody else," said Obama, on his first visit to the German capital as president.

"This is not a situation where we simply go into the Internet and start searching any way we want. This is a circumscribed system directed at us being able to protect our people and all of it is done under the oversight of the courts."

Obama was later due to speak to a crowd of roughly 4,000 invited guests at the Brandenburg Gate, which used to stand alongside the Berlin Wall dividing communist East Berlin from the capitalist West of the city.

His visit comes on the 50th anniversary of John F. Kennedy's famous "Ich bin ein Berliner" speech. Seizing on the Cold War theme, Obama is expected to announce plans to sharply reduce nuclear arms stockpiles, an initiative he kicked off with a speech in Prague in 2009 but which involves complex negotiations with Russia.

At the news conference, he touched on tensions with Afghan President Hamid Karzai over U.S. plans to begin talks with the Taliban to try to seek a negotiated peace after 12 years of war, acknowledging "huge mistrust" between the Western-backed government in Kabul and its arch-foes.

"We do think that ultimately we're going to need to see Afghans talking to Afghans about how they can move forward and end the cycle of violence there so they can start actually building their country," Obama said.

As a sign of displeasure with the U.S. move, Karzai has suspended talks with Washington on a troop agreement. But Obama said he welcomed Karzai's announcement that Afghan forces would soon take responsibility for security from the U.S.-led NATO peacekeeping force.

On Syria, Obama said reports that the United States was ready to "go all in" to war in the country were exaggerated. He reiterated his view that President Bashar al-Assad's government had used chemical weapons, while acknowledging that Russia was skeptical on this point.

For her part, Merkel said Germany would not deliver weapons to the rebels, even though a European Union arms embargo on Syria has lapsed.

Merkel election boost

Obama arrived in Germany from a two-day summit with Group of Eight leaders in Northern Ireland where he and other leaders clashed with Russian President Vladimir Putin over Syria.

He last came to Berlin in 2008, during his first campaign for the presidency. Back then, Merkel refused to allow him to speak at the Brandenburg Gate. Instead he spoke down the road in Berlin's Tiergarten park, attracting a crowd of 200,000 - largely enthusiastic admirers.

The Democrat has forged a pragmatic - if not warm - relationship with the conservative Merkel, who is hoping to get a boost out of the visit months before a German election.

In a message which seemed designed for her domestic audience, she told Obama at the news conference that balance was essential in government monitoring of Internet communications.

"I made clear that although we do see the need for gathering information, the topic of proportionality is always an important one and the free democratic order is based on people feeling safe," said Merkel, who grew up in the communist East and experienced the Stasi first hand.

Obama said the U.S. had thwarted at least 50 threats because of its monitoring program, including planned attacks in Germany.

"So lives have been saved and the encroachment on privacy has been strictly limited," he said.

A poll last week showed 82 percent of Germans approve of Obama, but the magic of 2008, when he was feted like a rock star, has faded amid concerns about his tactics in combating terrorism.

In a nod to the criticism, Obama defended his failure to close the Guantanamo Bay prison on Cuba that his predecessor George W. Bush opened after the invasion of Afghanistan in 2001, shortly after the September 11 attacks in New York and Washington.

He also reassured Germans that the U.S. military was not using German bases to launch unmanned drone attacks.

For Obama, who grew up in Hawaii and spent part of his childhood in Indonesia, Europe has sometimes seemed an after-thought. The signature foreign policy initiative of his first term was his "pivot" to Asia.

But analysts say plans to create a free-trade zone between the United States and European Union are a sign that he is repositioning policy to focus on Europe.

"The Obama administration has found it harder than expected to work with emerging powers and has fallen back to a more traditional reliance on European allies," said Charles Kupchan, professor of international affairs at Georgetown University.

"Washington doesn't have better options. And when it comes to who to engage in Europe, Germany grows stronger and stronger."

Obama spoke of "enduring bonds based on common values" that linked the United States to Europe.