Former Chancellor Helmut Kohl, who reunified Germany and pushed the country into the euro, urged Europe to press ahead with closer integration despite a crisis of the single currency, saying the continent must never again descend into conflict.

In a rare public appearance to mark 30 years since he became chancellor, Kohl was celebrated by party allies, an array of former presidents and prime ministers, as well as Angela Merkel, a former protégé with whom he has had a frosty relationship since she turned on him over a decade ago.

Frail since a fall in 2008 put him in the hospital for months, the 82-year old Kohl has remained largely silent through three years of euro turmoil, but on the occasions he has spoken out, he has voiced doubts about Merkel's handling of the crisis.

"Europe can never sink into war again," he told an audience at the German Historical Museum in Berlin. "We need to press ahead with the unification of Europe. Let's make good use of the time we have."

Before Kohl spoke, Merkel addressed the crowd, praising her former mentor's record but also defending her own approach to the crisis.

Merkel has demanded that struggling southern euro states introduce painful reforms in exchange for aid and talked tough with problem-countries like Greece. She has resisted pressure for "miracle solutions" like common euro zone bonds.

"The introduction of the euro was about stability and we feel an obligation here," she said. "We can't solve this crisis in one fell swoop. We need to take a considered approach."

Kohl was one of the towering European leaders of the second half of the 20th century. At the event on Thursday, he was praised in taped video tributes by former U.S. President George H.W. Bush, Britain's John Major, France's Edouard Balladur and Israel's Shimon Peres.

Yet his legacy has been recast, revised and redrawn many times over the past decades and its final chapter has probably not been written.

Reunification and the euro

In Germany and abroad, he is celebrated as the father of German reunification, though his promise of "flourishing landscapes" in the east failed to materialise.

Kohl's other landmark achievement, pushing through the euro together with French President Francois Mitterrand, was hailed as a huge success in the currency's first decade. But it looks less glorious after three years of crisis that have raised the prospect of a catastrophic euro breakup.

Some in Germany now blame Kohl for pressing ahead with the euro without insisting on closer political and fiscal integration as a condition – a decision that Merkel has denounced publicly as an epic mistake.

Kohl's defenders point out that it was his successor as chancellor, Gerhard Schroeder, who allowed Greece into the bloc and watered down EU budget rules.

Another black mark on Kohl's record is the party funding scandal that soured his relationship with Merkel, whom he'd plucked from obscurity after the Berlin Wall fell and brought into his cabinet.

It was Merkel who engineered her party's break from Kohl, urging the Christian Democratic Union (CDU) to move on "without its old war horse" when the scandal erupted.

But enough time has now passed for both to have recognised the benefits of a rapprochement.

"This is an attempt at reconciliation," Gerd Langguth, a professor at Bonn University said of Thursday's event. "Both sides realise it is time for Kohl to return to the bosom of the party."

Merkel may also hope that bringing him back into the fold will help unify the CDU in the run-up to an election next year in which she will fight for a third term. Some believe the event may be the start of a rebranding of Merkel as a "great European" in the tradition of Kohl and Konrad Adenauer.

"So far, Merkel hasn't told the right story to the German people," a former minister in Kohl's cabinet who attended Thursday's event told Reuters on condition of anonymity.

"Her message has been that Germany is right and others in Europe must become like us. This will never happen. We cannot Germanise Europe. Kohl understands this. We can only hope this event is a sign that Merkel is beginning to realise that too."