President Bush said he could consider using force as a last resort to press Iran to give up its nuclear program.
But German Chancellor Gerhard Schroeder, one of the most prominent European opponents of the U.S.-led war on Iraq, told an election rally on Saturday the threat of force was not acceptable.
In what appeared to be a reference to Bush's remarks that "all options are on the table," Schroeder told the crowd in his home city of Hanover:
" ... let's take the military option off the table. We have seen it doesn't work."
Iran angered the European Union and the United States by resuming uranium conversion at the Isfahan plant last Monday after rejecting an EU offer of political and economic incentives in return for giving up its nuclear program.
Tehran says it aims only to produce electricity and denies Western accusations it is seeking a nuclear bomb.
The EU -- represented by Britain, France and Germany -- has been trying to find a compromise for two years between arch foes Iran and the United States.
Bush, speaking at his ranch in Crawford, Texas, was asked in the interview broadcast on Saturday whether possible options included the use of force.
"As I say, all options are on the table. The use of force is the last option for any president and you know, we've used force in the recent past to secure our country," he told state-owned Israel Channel One television.
Washington last week expressed a willingness to give negotiations on Iran's suspected nuclear weapons program more time before getting tougher with the country, and Bush made clear he still hoped for a diplomatic solution.
"In all these instances we want diplomacy to work and so we're working feverishly on the diplomatic route and we'll see if we're successful or not," Bush said in the Israeli interview.
Bush has also previously said that the United States has not ruled out the possibility of military strikes. But U.S. officials have played down media speculation earlier this year they were planning military action against Iran.
French Foreign Minister Philippe Douste-Blazy said on Friday that negotiations were still possible with Iran on condition the Iranians suspend their nuclear activities.
The governing board of the International Atomic Energy Agency unanimously called on Iran on Thursday to halt sensitive atomic work.
If Iran continues to defy global demands, another IAEA meeting will likely be held, where both Europe and Washington will push for a referral to the U.N. Security Council for possible sanctions.
Schroeder, whose Social Democrats are lagging the opposition conservatives in opinion polls ahead of September elections, said he was worried about developments in Iran because no one wants it to gain possession of atomic weapons.
"The Europeans and the Americans are united in this goal. Up to now we were also united in the way to pursue this," he said.
Schroeder's opposition to the Iraq war was seen as a decisive factor in his unexpected victory in the 2002 general election, which he won narrowly after coming from behind.
But his critical stance caused serious ruptures in Germany's traditionally strong relations with the United States.