German Chancellor Olaf Scholz and French President Emmanuel Macron met on Sunday to recommit to the alliance their nations created after the Second World War, despite strain caused by Russia's invasion of Ukraine.
Despite mounting pressure on Berlin to supply Ukraine with German Leopard tanks, Mr Scholz stopped short of any pledge, instead insisting all allies must work together.
Although France is already sending light tanks to Ukraine, Mr Macron made it clear that "nothing is excluded" on the possible delivery of French-made Leclerc heavy tanks.
Mr Scholz was visiting Paris to celebrate 60 years of post-war co-operation at a time when the Franco-German relationship, often described as the motor of Europe, has come under unusual strain.
On top of French impatience with Germany's caution on Ukraine, differences on nuclear power, budget problems and a possible lack of personal chemistry between the two men have caused tensions.
But in a speech at the capital's Sorbonne University, Mr Scholz said upholding strong ties was key for the continent.
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"The future, like the past, rests on co-operation between both our countries as the driving force of a united Europe," he said.
Mr Macron said: "Germany and France, because they cleared the path to reconciliation, must become pioneers to relaunch Europe.
"We are two souls in the same body."
Germany has so far resisted Ukrainian pleas for the Leopard 2 tanks, with reports suggesting it would only agree if the US followed with a similar move.
Mr Scholz said that the country had always acted "in close co-ordination with our friends and allies".
He refused to be drawn on the request for the tanks.
"We fear that this war is going to last for a long time," Mr Scholz said. "We are only going to act in close co-ordination."
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But Mr Macron, who this month agreed to send French-made AMX-10 RC light tanks to Ukraine, indicated that France was considering sending the heavy tanks to Ukraine.
"As for the Leclercs, I have asked the Defence Ministry to work on it. Nothing is excluded," he said.
Mr Macron said any effort to send the hardware to help repel the Russian invasion should be decided and co-ordinated "collectively" with allies including Germany.
He said any joint decision on whether to send heavy tanks depended on three criteria.
They were that it did not "escalate" the conflict, that it provided "real and effective support" to Kyiv's forces, including in view of how long it would take to train Ukrainians, and that it "not weaken our own defence capabilities".
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Adding to the pressure on Berlin, Prime Minister Mateusz Morawiecki of Poland described Germany's attitude as "unacceptable".
"Innocent people are dying every day," Mr Morawiecki told the Pap news agency.
Germany's Foreign Minister, Annalena Baerbock, said on Sunday that her government would not stand in the way if Poland wanted to send its Leopard 2 tanks to Ukraine.
Ukrainian officials have been calling on western allies to supply them with the modern German-made tanks for months, but Berlin has so far held back from sending them or allowing other Nato countries to do so.
Asked what would happen if Poland sent its Leopard 2 tanks without German approval, Ms Baerbock told France's LCI TV: "For the moment the question has not been asked, but if we were asked we would not stand in the way."
The 1963 Elysee Treaty signed between post-Second World War German and French leaders Konrad Adenauer and Charles de Gaulle provided for matters ranging from military co-operation to youth exchanges.
Since then, France and Germany have often built the foundation for joint crisis response in Europe, and other nations are looking to them again now.
"We will continue to provide Ukraine with all the support it needs for as long as necessary, together as Europeans to defend our European peace project," Mr Scholz said at the Sorbonne.
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Top issues at the meeting also included climate and energy, and European competitiveness faced with a new wave of "buy-American" subsidies in the US.
Leaders across Europe fear distortions in transatlantic trade from the Inflation Reduction Act, which will pour billions of dollars into American-made, climate-friendly technology.
After securing backing from Spanish leader Pedro Sanchez this week, Mr Macron said France and Germany had agreed on a "common line" in an "ambitious and rapid" European response to the American subsidies.