Obama noted that America and Europe should unite more to tackle international issues like terrorism, the Middle East and Iran.

A street performer stands with US flag in front of the Brandenburg Gate in Berlin July 24, 2008. (Xinhua/Reuters Photo) 

"No one welcomes war. I recognize the enormous difficulties in Afghanistan, but my country and yours have a stake in seeing that NATO's first mission beyond Europe's borders is a success," he said.

"For the people of Afghanistan, and for our shared security, the work must be done. America cannot do this alone," he added.

Obama also said Iran should "abandon nuclear ambition" and called for a "world without nuclear weapons," which won widespread cheers from crowds.

Obama said he was speaking as a citizen, not as a president, but local media compared his speech to historic speeches in the same place by US Presidents John F. Kennedy and Ronald Reagan.

(Xinhua News Agency July 25, 2008)