Iran could have nuclear weapons within the next 10 years, according to the senior US intelligence chief.
Director of National Intelligence John Negroponte told BBC Radio's Today programme his assessment was that Iran was actively trying to make weapons, reports Trend.
His comments come after UN Security Council members agreed a "far-reaching" plan to persuade Tehran to suspend its nuclear programme.
The UK said the Security Council would take action if Iran did not comply.
Iran resumed enrichment of uranium this year and maintains its nuclear activities are aimed at energy production. Lessons learned
In his interview with the BBC, Mr Negroponte accused Iran of being the world's top state sponsor of terrorism.
He added: "[Iran] seems to be determined to develop nuclear weapons.
"We don't have a clear-cut knowledge but the estimate we have made is some time between the beginning of the next decade and the middle of the next decade they might be in a position to have a nuclear weapon, which is a cause of great concern."
Mr Negroponte also acknowledged that US intelligence had made mistakes assessing the weapons capabilities of Iraq before the invasion, but said lessons had been learned and corrective measures taken.
He said: "I think we have improved the integrity of our analyses substantially. I think we have internalised some of these lessons." 'Significant benefits'
In Vienna on Thursday, six major world powers agreed a package of incentives and penalties to try to induce Iran to curb its nuclear programme.
The proposals will be raised with Tehran in the coming days.
Although no details have been made public, sources say they could include giving Iran a nuclear reactor and an assured supply of enriched uranium.
All Security Council action could also be suspended upon compliance.
UK Foreign Secretary Margaret Beckett called the incentives "far-reaching".
She said: "There are two paths ahead. We urge Iran to take the positive path and consider seriously our substantive proposals which would bring significant benefits to Iran."
US officials said Iran would have just weeks to decide whether to accept the package.
There has been no official reaction yet from Iran.