Clinton's appeal in Berlin comes as President Barack Obama's administration mulls a new strategy for Afghanistan and seeks greater European support for defeating the Islamist extremists who are gaining ground in that country.

"Our history did not end the night the wall came down," Clinton told current and former European and US political heavyweights on the eve of the 20th anniversary of an event that symbolised the end of the Cold War.

"It began anew," Clinton said in a key-note speech hosted by the Atlantic Alliance.

"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," she said.

The chief US diplomat recalled how German Chancellor Angela Merkel, during a visit to Washington last week, spoke of the walls of the last century and "the less visible but equally daunting walls" of today.

"These are walls between the present and the future, walls between modernity and nihilistic attitudes, walls that divide our common heart, that deny progress and opportunity to the many who yearn for both," Clinton said.

Clinton highlighted the moment that Merkel will on Monday walk through the heart of once-divided Berlin as a moment that "should be a call to action, not just a commemoration of past actions.

"That call should spur us to continue our cooperation and to look for new ways that we can meet the challenges that freedom faces now," Clinton said.

"We owe it to ourselves and to those who yearn for the same freedoms that are enjoyed and even taken for granted in Berlin today," she said.

"And we need to form an even stronger partnership to bring down the walls of the 21st century and to confront those who hide behind them: the suicide bombers, those who murder and maim girls whose only wish is to go to school," she said.

"In place of these new walls, we must renew the trans-Atlantic alliance as a cornerstone of a global architecture of cooperation," Clinton said.

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