Berlin -- The united Germany remains marred by division 20 years after the fall of the Berlin Wall, Chancellor Angela Merkel said Monday as she set off emotional commemorations of the defining moment in the end of communism in Europe.

Thousands thronged the route of the Wall in Berlin -- ripped down by East Germans on the night of November 9 1989 -- as Merkel attended a "very moving" memorial service at a church where pro-democracy rallies were held in the weeks before the end of the communist regime.

The chancellor gave her warning about the work still to be done before the main ceremonies at the historic Brandenburg Gate with British Prime Minister Gordon Brown, presidents Nicolas Sarkozy of France and Dmitry Medvedev of Russia and US Secretary of State Hillary Clinton.

Former Soviet leader Mikhail Gorbachev, ex-Polish president Lech Walesa and dissidents who helped end European communism will also be on hand at the former "death strip" where border guards once had shoot-to-kill orders.

"German unity is still incomplete," said Merkel, who grew up behind the Iron Curtain in communist East Germany.

"We must tackle this problem if we want to achieve equal quality of life" in east and west, she told ARD public television, noting that unemployment was still twice as high in the depressed east than in the west.

At a ceremony late Sunday, Clinton issued a call for a new transatlantic push to free those still oppressed.

"Our history did not end the night the Wall came down," she said.

"To expand freedom to more people, we cannot accept that freedom does not belong to all people. We cannot allow oppression defined and justified by religion or tribe to replace that of (communist) ideology."

Following weeks of protests against the regime, East Germany's Stalinist authorities suddenly opened the border on November 9, 1989.

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

In a tribute to be delivered at the Brandenburg Gate, Brown called the unity of Berlin, Germany and Europe "majestic" achievements.

The Wall "was swept away by the greatest force of all -- the unbreakable spirit of men and women who dared to dream in the darkness," he said.

But Medvedev said Russia had often felt on the backfoot since the Wall fell, despite assurances at the time that NATO would not expand eastward.

"We believed that as the result of the fall of the Berlin Wall Russia's place in Europe would be defined somewhat differently," he told Germany's Der Spiegel magazine.

"We were hoping the disappearance of the Warsaw Pact would be accompanied by a different degree of Russia's integration into common European space. What have we received as a result? NATO is still a bloc whose rockets are targeting the Russian territory."

Merkel, Walesa and Gorbachev, who remains a revered figure here, will join former dissidents in crossing the former checkpoint at Bornholmer Strasse, where hundreds of East Germans had their first taste of freedom.

The celebrations will later move to the Brandenburg Gate for an open-air concert and the symbolic toppling of 1,000 giant styrofoam dominoes along two kilometres (1.2 miles) of the Wall's former course.

An overwhelming majority of Germans are still grateful for the Wall's fall, according to a poll in the Leipziger Volkszeitung daily, with 79 percent of those surveyed calling November 9, 1989 a joyous day.

But sociologist Frithjof Hager of Berlin's Free University said national unification, sealed in 1990, was still a work in progress.

"I believe the authoritarian mindset is still an issue (in the east) -- such things only change very slowly," he told AFP. "But I think simply pointing the finger at easterners would be deeply unfair."

South Korean activists marked the anniversary in Seoul by launching leaflets attacking North Korea's leader across the world's last Cold War frontier.

"Down with Kim Jong-Il's Songun dictatorship," they shouted in reference to the leader's army-first policy which prioritises the welfare of troops over civilians.

AFP/Expatica