A draft UN resolution on new sanctions against Iran will include calls for trade curbs and a travel ban for Iran's nuclear scientists, diplomats say.
China and Russia had questioned the need for more sanctions on Iran
The US, UK, France, Russia, China and Germany have agreed to put the draft measures to the UN security council, the BBC's Laura Trevelyan has learned.
Two sets of UN sanctions have already been imposed on Iran, to punish it for continuing to enrich uranium.
Iran denies claims that it wants to use the technology to build a nuclear bomb.
The proposed sanctions include calls for restrictions on government-backed trade with Iran, and also cargo controls to ensure countries are not selling anything to Iran which would help it make a nuclear bomb.
It has taken the five permanent Security Council members and Germany months to agree the measures.
"We are hoping for another consensual resolution that makes clear to Iran that its continued disregard for council resolutions is not tolerable," US envoy to the UN Alejandro Wolff told AFP news agency.
"We are looking forward to getting this done in a matter of a few weeks," he added.
Tehran says its purposes are entirely civilian
Nicholas Burns, the US Assistant Secretary of State, told the news agency that the new resolution was intended to punish Tehran.
"This is a punitive resolution. I say this because I saw some comments yesterday from Moscow that it wasn't. It is," Mr Burns said.
He was responding to comments by Russian Foreign Minister Sergei Lavrov that the agreed draft did not require tough new measures against Tehran.
Previous sanctions on Iran included a ban on the sale of any material which might help Iran develop an atomic weapon, and a freeze on the financial assets of people and banks thought to be involved in Iran's nuclear work.
Iran insists its nuclear programme is for civilian energy, not military purposes.
But it continues to enrich uranium, a process which can lead to the development of a nuclear bomb.
Western diplomats admit the agreed draft resolution is a compromise, our correspondent reports.
The US and its European allies wanted tougher measures, but Russia and China, who have significant trade links with Iran, did not.
The US attempt to push for stronger Security Council sanctions was further undermined by the country's own national intelligence estimate, published in late 2007, which said Iran stopped its nuclear weapons programme in 2003.
It may not be easy for the six powers to get a resolution against Iran through the Security Council, our correspondent adds, as Libya, Indonesia, Vietnam and South Africa could all object.