US Secretary of State Condoleezza Rice has warned Iran it faces possible UN sanctions unless it accepts a European deal on its nuclear programme.
Rice is on a fence-building mission, correspondents say
If Iran is "unwilling to take the deal... then the Security Council looms," Ms Rice told Fox News.
Britain, France and Germany have offered Iran trade concessions if it gives up its nuclear programme.
Ms Rice was speaking as she and Defence Secretary Donald Rumsfeld were due in talks with European allies.
Ms Rice is meeting EU and Nato officials in Brussels, and Mr Rumsfeld is meeting Nato defence ministers in Nice.
The Secretary of State is nearing the end of an eight-day tour of Europe and the Middle East, during which she has sought to bury differences with Europe over Iraq, says the BBC's Europe correspondent Tim Franks in Brussels.
Iran has agreed to temporarily suspend its uranium enrichment activities during the negotiations process with Europe.
RICE'S SEVEN-DAY TOUR
Fri: Met UK's Tony Blair and Foreign Secretary Jack Straw in London; talks with Germany's Gerhard Schroeder in Berlin
Sat: Talks with leaders in Germany, Poland and Turkey; met Russian foreign minister in Ankara
Sun: Met Turkish government, then on to Israel to meet Ariel Sharon
Mon: Talked with Mahmoud Abbas in West Bank
Tue: Met with Italian counterpart in Rome, then on to Paris to deliver speech
Wed: Talks with French ministers, then on to meet Nato and EU officials in Brussels and Luxembourg
Thurs: Returns to Washington
Iran says its nuclear programme is peaceful, but the US claims Iran is on the path to developing nuclear weapons.
"They [Iran] need to hear that the discussions they are in with the Europeans are not going to be a kind of way-station, where they are allowed to continue their activities," Ms Rice said in an interview with the US television network.
"I don't know that anyone has said that as clearly as they should to the Iranians," she said.
Iran has signed the Nuclear Non-Proliferation Treaty (NPT), which prohibits the development of atomic weapons.
The UN's Security Council has the power to impose stringent sanctions on Iran if it is found to be in breach of the treaty.
In Nice, Mr Rumsfeld is expected to call on Nato colleagues to do more for the military effort in Iraq.
Nato said it would contribute 300 personnel for a training mission, but so far there are fewer than 100 on the ground.
The US-led invasion of Iraq during US President George Bush's first term badly strained ties with Europe.
Some countries, notably France and Germany, said they would have nothing to do with operations in Iraq. Spain initially sent troops but then decided to pull them out.
Ms Rice's meeting with EU officials is expected to touch on Iran, and EU plan to lift an embargo on arms sales to China - a plan which the US deplores, our correspondent says.