COMMON VALUES

In his speech to 4,000 invited guests at the Brandenburg Gate, Obama harked back to Kennedy by stressing what he called common values of openness and tolerance.

"We can be a little more informal among friends," he joked as he took off his jacket in the sweltering sun on the Pariser Platz square, just east of the Gate that once stood alongside the Berlin Wall dividing the communist East from the capitalist West of the city.

Earlier, at the news conference, he touched on tensions with Afghan President Hamid Karzai over US 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.

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 sceptical on this point.

Obama declined to give specifics on new military aid Washington plans to provide to Syrian rebels.

Obama arrived in Germany after 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.

Despite these divisions, he said he would engage with Moscow on reducing deployed nuclear weapons by up to a third from previously agreed levels.

"I intend to seek negotiated cuts with Russia to move beyond Cold War nuclear postures," Obama said.

In 2008, Merkel refused to allow Obama, then a senator from Illinois, to speak at the Brandenburg Gate because he was not yet president.

Despite this awkward start, the Democrat has forged a pragmatic relationship with the conservative Merkel, who may be hoping for a political boost out of the visit months before a German election.

DRONES

In a nod to 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 US 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 focusing more 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."