Former Soviet leader Mikhail Gorbachev warned in a speech in Berlin on Saturday that East-West tensions over the Ukraine crisis were threatening to push the world into a new Cold War, 25 years after the fall of the Berlin Wall.

Gorbachev, who is credited with forging a rapprochement with the West that led to the demise of communist regimes across Eastern Europe, accused the West, and the United States in particular, of not fulfilling their promises after 1989.

"The world is on the brink of a new Cold War. Some say that it has already begun," said Gorbachev, who is feted in Germany for his pivotal role in helping create the conditions for the Berlin Wall's peaceful opening on Nov. 9, 1989, heralding the end of the Cold War.

"And yet, while the situation is dramatic, we do not see the main international body, the U.N. Security Council, playing any role or taking any concrete action."

The conflict in eastern Ukraine has killed more than 4,000 people since the start of an uprising by pro-Russian separatists in mid-April.

Russia blames the crisis on Kiev and the West, but Nato says it has overwhelming evidence that Russia has aided the rebels militarily in the conflict.

Gorbachev, 83, also criticised Europe and said it was in danger of becoming irrelevant as a global power.

"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," he said.

"The consequence inevitably is Europe weakening at a time when other centres of power and influence are gaining momentum. If this continues, Europe will lose a strong voice in global affairs and gradually become irrelevant."

Speaking at an event at Berlin's Brandenburg Gate, Gorbachev said the West had exploited Russia's weakness after the collapse of the Soviet Union in 1991.

"Euphoria and triumphalism went to the heads of Western leaders," he said. "Taking advantage of Russia's weakening and the lack of a counterweight, they claimed monopoly leadership and domination of the world, refusing to heed words of caution from many of those present here," he said.

Gorbachev said the West had made mistakes that upset Russia with the enlargement of NATO, with its actions in the former Yugoslavia, Iraq, Libya and Syria and with plans for a missile defence system.

"To put it metaphorically, a blister has now turned into a bloody, festering wound," he said. "And who is suffering the most from what's happening? I think the answer is more than clear: It is Europe." – Reuters