German Chancellor Gerhard Schroeder has warned the US to back away from the possibility of military action against Iran over its nuclear programme.
His comments come a day after President Bush reiterated that force remained an option but only as a last resort.
Iran has resumed what it says is a civilian nuclear research programme but which the West fears could be used to develop nuclear arms.
Germany, France and the UK have led efforts to end the crisis peacefully.
Mr Schroeder directly challenged Mr Bush's comment that "all options are on the table" over the Iran crisis.
"Let's take the military option off the table. We have seen it doesn't work," Mr Schroeder told Social Democrats at the rally in Hanover, to rapturous applause from the crowd.
Mr Schroeder said it remained important that Iran did not gain atomic weapons, and a strong negotiating position was important.
"The Europeans and the Americans are united in this goal," he said. "Up to now we were also united in the way to pursue this."
"This is why I can with certainty exclude any participation by the German government under my direction," Mr Schroeder tells the paper.