US President George W Bush and German Chancellor Gerhard Schroeder have put aside their differences over Iraq and pledged to focus on areas of agreement.
The two leaders are looking to move on from past disagreements
They united in warning Iran not to develop nuclear weapons and sought to play down differences in approach.
Following talks in the German city of Mainz, Mr Bush said the world should "speak with one voice" on Iran.
The president is on the third day of a European tour designed to reconcile transatlantic differences.
"We have agreed not to emphasise those areas where we disagree," Mr Schroeder said at the start of a joint news conference.
Mr Bush praised the German contribution to Iraq's reconstruction, and thanked Germany for helping lead diplomatic efforts with Iran.
"We just started the diplomatic efforts and I want to thank our friends for taking the lead. We will work with them to convince the mullahs that they need to give up their nuclear ambitions," he said.
Monday: Talks with Belgian leaders and a speech on transatlantic relations. Dinner with French President Jacques Chirac
Tuesday: Breakfast with UK Prime Minister Tony Blair. Meets Ukrainian and Italian leaders at Nato HQ, then meets EU leaders
Wednesday:Talks in Germany with Chancellor Gerhard Schroeder, then meets US troops in Wiesbaden
Thursday: Gives speech in Slovak capital, Bratislava, meets Russian President Vladimir Putin
Mr Schroeder said: "We absolutely agree that Iran must say no to any kind of nuclear weapons."
Germany, the UK and France are trying to persuade Iran to give up its nuclear enrichment programme in return for political and economic benefits.
The US does not have diplomatic relations with Iran, which it accuses of trying to develop a nuclear weapon.
Iran has insisted its nuclear programme is for peaceful, civilian use only, but it has agreed to a temporary freeze on enrichment during its negotiations with the Europeans.
Mr Bush again sought to ease European worries that the US is planning to use military force against Iran, saying "Iran is not Iraq".
But he repeated that all options were on the table, a difference with the German position that rules out the use of force.
The BBC's Ray Furlong, in Germany, says the central theme of Mr Bush's trip - that the Atlantic alliance is alive and well - was reinforced.
But ordinary Germans are still deeply sceptical, our correspondent says.
An opinion poll released just as the president arrived suggests that more Germans trust Russian President Vladimir Putin than the US president.
Not all Germans are happy about President Bush's visit
As the German and US leaders met, anti-war campaigners held a protest against the US-led war in Iraq.
Other topics discussed between the two leaders included the Middle East peace process and the role of Nato.
The two leaders acknowledged their differences on the Kyoto climate change treaty - which has come into force without US support - but said they would still work together for a better environment.
They signed a joined declaration promising to co-operate on reducing environmental pollution and greenhouse gas emissions.
Our correspondent says that despite the two leaders' attempts to present a united front, there are clear disagreements between them.
The German leader has called for an overhaul in the way Nato operates, to give Europe more of an equal voice - a suggestion criticised by US officials as "clumsy".
And Germany and France want to lift the arms embargo on China and sell weapons to the communist state, despite US opposition.