Former Soviet leader Mikhail Gorbachev says tensions between Russia and the West over the Ukraine crisis have put the world "on the brink of a new Cold War."
Gorbachev, 83, spoke on November 8 at an event in the German capital marking the 25th anniversary of the fall of the Berlin Wall.
Gorbachev accused the West -- particularly the United States -- of giving in to "triumphalism" after the collapse of the communist bloc.
For that reason, he added, the global powers have been unable to cope with conflicts in Yugoslavia, the Middle East, and now Ukraine.
More than 4,000 people have died since April in the fighting between government troops and pro-Russian separatists in eastern Ukraine.
Gorbachev said that "Instead of becoming a leader of change in a global world, Europe has turned into an arena of political upheaval, of competition for spheres of influence, and finally of military conflict. The consequence inevitably is Europe weakening."
"Bloodshed in Europe and the Middle East against the backdrop of a breakdown in dialogue between the major powers is of enormous concern," he added.
The last leader of the Soviet Union called for trust to be built through dialogue with the Kremlin.
He also suggested the United States and the European Union should lift sanctions against Russian officials -- imposed over the annexation of Crimea in March and Moscow's alleged involvement in the Ukraine conflict.
The three-day celebrations in Germany are remembering the peaceful revolution that led East German border guards to open the gates to West Berlin on November 9, 1989, allowing free passage to large crowds. The East German authorities had built the Berlin Wall in August 1961 to halt a mass exodus to the West.
Germany reunited the following year, on October 3, 1990.
Festivities will conclude at the Brandenburg Gate, the symbol of German unity, on November 9 to mark exactly 25 years since Germany's Cold War divisions were breached.
Gorbachev and former Polish president and freedom icon Lech Walesa are among those due to attend a show that will include a rock concert and fireworks.
With reporting by AP and dpa