Permanent members of the UN Security Council - and Germany - have agreed on the contents of a new draft resolution of fresh sanctions against Iran.
Tehran insists that its nuclear programme is entirely peaceful
The announcement was made by the German foreign minister after talks in Berlin with his counterparts from the US, France, the UK, Russia and China.
The US and its European allies want a third set of sanctions over Iran's refusal to suspend uranium enrichment.
Iran insists its nuclear programme is for energy, not military purposes.
"Today we together agreed on the content of such a new resolution," German Foreign Minister Frank-Walter Steinmeier said afterwards.
He said it would be submitted by Germany, France and the UK, for discussion by the full Security Council.
A US official said the resolution would "increase the severity" of existing sanctions, such as travel bans and asset freezes, "and will also introduce new elements".
However a European diplomat, quoted anonymously by the Associated Press, said there would be no new sanctions as such.
The US official said: "The US is very pleased."
"This is a swift reminder to the Iranians that they are not in compliance," he said, adding: "The six powers are united."
The Western countries have been keen to crank up the pressure further on Iran, but China and Russia have been reluctant to introduce more punitive measures.
Convincing Beijing and Moscow to sign up to a new wave of UN sanctions was made more complicated last month by the publication of an American intelligence report which declared that Iran had halted its nuclear weapons programme in 2003.
Tehran has repeatedly said penalties will not force it to halt its uranium enrichment.
"Adoption of a possible new resolution will not have any effect on our people," government spokesman Gholam Hossein Elham said on Tuesday.
Iran says it simply wants to generate electricity and denies claims by the White House and key allies that it is building a nuclear bomb.