Obama in surprise Berlin Wall video address

US President Barack Obama on Monday made a surprise video address to celebrations in Germany marking the 20th anniversary of the fall of the Berlin Wall.

"There could be no clearer rebuke of tyranny. There could be no stronger affirmation of freedom," Obama said of the fall of the concrete barrier that divided East and West Berlin for 28 years until November 9, 1989.

In the message beamed into celebrations at Berlin's Brandenburg Gate, once on the border between East and West Berlin, Obama told cheering crowds: "Even in the face of tyranny. People insisted that the world could change."

"Even as we celebrate these values, even as we mark this day, we know the work of freedom is never finished."

The video was played after German Chancellor Angela Merkel, who grew up in the state of Brandenburg in communist East Germany, led leaders including Russian President Dmitry Medvedev through the Gate.

"Few would have foreseen ... that a united Germany would be led by a woman from Brandenburg or that their American ally would be led by a man of African descent. But human destiny is what human beings make of it," Obama said.

Secretary of State Hillary Clinton represented the United States at Monday's ceremonies, which also included French President Nicolas Sarkozy and Britain's Prime Minister Gordon Brown.

Obama added: "Today, there are still those who live within the walls of tyranny. Human beings that are denied the very human rights that we celebrate today. That is why this day is for them as much as it is for us."

"It is for those who believe that in the face of cynicism, doubt and oppression, that walls can truly come down."

"Let us never forget November 9, 1989, nor the sacrifices that made it possible... together, let us keep the light of freedom burning bright for all who live in the darkness of tyranny and believe in the hope of a brighter day."

Following weeks of protests against the regime, East Germany's Stalinist authorities suddenly allowed people to travel to the West on November 9, 1989.

After 28 years as prisoners in their own country, East Germans streamed to checkpoints and rushed past bewildered guards, many falling tearfully into the arms of West Germans on the other side.

Eleven months later, East and West Germany unified.