Germany celebrates fall of Berlin Wall

US President Barack Obama has 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, Mr 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', he said.

Meanwhile, German Chancellor Angela Merkel joined former Soviet leader Mikhail Gorbachev for celebrations to mark the 20th anniversary of the fall of the Berlin Wall.

View a gallery of pictures from 1989

Europe's Revolution - 20 years on: Read Tony Connelly's account of his journey through eastern Europe to mark the anniversary

Ms Merkel, who grew up in the communist state, Mr Gorbachev and ex-Polish president Lech Walesa have passed through what used to be the Bornholmer Strasse border crossing, where euphoric easterners first went to the West that night.

'It is not only a day of celebration for Germans. It is a day of celebration for the whole of Europe,' she said.

Earlier Ms Merkel attended a 'very moving' memorial service at a church where pro-democracy rallies were held in the weeks before the wall was opened, and lamented the enduring scars of the country's postwar division.

'German unity is still incomplete,' Ms Merkel told ARD public television, noting how east Germany still lagged behind the west in economic growth, with joblessness nearly twice as high.

'We must tackle this problem if we want to achieve equal quality of life.'

Taoiseach Brian Cowen, French President Nicolas Sarkozy, Russian President Dmitry Medvedev, British Prime Minister Gordon Brown and US Secretary of State Hillary Clinton are among those taking part in the commemorations hosted by Ms Merkel.

The main ceremony begins at the Brandenburg Gate at 6pm tonight and will be followed by a formal dinner at the chancellery.

Thousands of tourists have poured into the city to mark the event that hastened the reunification of Germany, the collapse of the Iron Curtain and the end of the Soviet Union.

In a speech in Berlin this afternoon Ms Merkel said: 'The night of 9 November 1989 was the fulfilment of a dream.

'Many played a role. But it would not have been possible without the courage of the people in the former East Germany.'

Ms Merkel, who was working as a scientific researcher in East Berlin at the time, said at the weekend that the fall of the wall was 'the happiest day in recent Germany history'.

She told a newspaper that she was sticking to her usual Thursday night routine of taking a sauna on the night the wall fell.

Celebrations are planned all over the city, including the toppling of 1,000 giant brightly coloured dominoes along a 1.5km stretch of the wall's original path.

Communist East Germany began erecting its 'anti-fascist protection barrier' in the early hours of 13 August 1961.

According to a study published this year, at least 136 people were killed at the Berlin Wall between 1961 and 1989 while trying to escape.

In November 1989, following weeks of protests against the regime, East Germany's Stalinist authorities suddenly allowed people to travel to the West that autumn evening.

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

Behind the scenes, the celebrations will also allow the visiting European leaders to consider the future direction of the continent following the signing of the EU's Lisbon Treaty.

It is expected there will be discussions in the margins over the allocation of the new posts of president and high representative - effectively EU foreign minister - created by the treaty.