On the flight from Israel to Germany, Obama said he wanted the US and Europe to rediscover their common ground.
"There is no doubt that part of what I want to communicate on both sides of the Atlantic is the enormous potential of us restoring a sense of coming together," he said.
He played down comparions with the late president John F Kennedy's "Ich bin ein Berliner" vow to the then-divided city in 1963, or Ronald Reagan's call in 1987 to "Tear down this wall".
"They were presidents, I am a citizen," he said.
But Obama defended himself against claims that he is defying convention by campaigning abroad, saying he wanted to speak to the whole of Europe so he needed a big venue.
"The people in the crowd are not voters, in that sense, it is not designed to get them to the polls," he said.
"It is not a political rally, hopefully it will be viewed as a substantive articulation of the relationship I would like to see between the United States and Europe."
'Two state' commitment
Obama said on Wednesday that he backed Israel's decision not to negotiate with the Palestinian group Hamas, in a visit to Israel and the West Bank.
Speaking in the town of Sderot, which has been hit by rocket attacks from Hamas-controlled Gaza, Obama said the US also supported Israel's right to defend itself "against those who threaten its people".
|Obama met Merkel and other German officials after arriving in Berlin [AFP]
He also reiterated his position that Jerusalem "will be" the capital of Israel.
But Obama said that he believed the city to be a "final status issue" that must be decided by negotiation and said he remained committed to a two-state solution to the conflict.
The status of Jerusalem remains one of the most contentious parts of any solution to the Middle East conflict.
In June Obama caused anger in the Arab world when he said that Jerusalem should be Israel's undivided capital.
The international community, including the United States, does not recognise Israel's claim that Jerusalem is its undivided capital and Palestinians hope to have East Jerusalem, currently occupied by Israel, as the capital of any future Palestinian state.
Obama also said that he would take "no options off the table" with regards to Iran, saying the country posed a "grave threat".
"A nuclear Iran would be a game-changing situation, not just in the Middle East but around the world," Obama said.
|Obama travelled to the West Bank,
unlike his rival John McCain [AFP]
The Illinois senator, who had earlier held talks with Palestinian leaders in the West Bank city of Ramallah, said that if he was elected he would adopt a policy of "big sticks and big carrots" regarding the Iranian government.
"I would at my time and choosing be willing to meet with any leader if I thought it would promote the national security interest of the United States of America," he said.
Obama travelled from Jerusalem to the West Bank city on Wednesday for talks with Mahmoud Abbas, the Palestinian president, and Salam Fayyad, the prime minister, before heading to Sderot.
Mustafa Barghouti, the secretary of the Palestinian Initiative, told Al Jazeera that as the candidate of change, Obama should also bring change to the Middle East.
"He cares a lot about the Jewish vote but it is time to care about the Arab vote and the Muslim vote," he said.
"The whole stability of the Middle East depends on resolving the Palestinian issue."
Later Obama told Ehud Olmert, the Israeli prime minister, that he had an "unshakeable commitment to Israel's security".