The US official said the outcome of the meeting flew in the face of Iranian claims that the sanctions issue had driven a wedge through the powers.
"This is the answer to Tehran. The US is very pleased," he said.
The official said that the foreign ministers of the six countries (Britain, Russia, China, France, the US and Germany) had four technical issues to resolve as they sat down to the talks but had ironed out their differences during the course of the two-hour meeting.
He said the group had agreed not to distribute the text before presenting it to the other 10 members of the Security Council.
The ministers were to continue their talks over dinner in the German capital on Tuesday.
Washington and its EU allies have recently been pushing for a third set of economic and trade sanctions against Iran for defying international demands to stop uranium enrichment activities that they fear could be used to make a bomb.
Iran denies it is seeking an atomic weapon, insisting its nuclear programme is peaceful and aimed merely at providing energy for its growing population.
China and Russia, which have lucrative trade ties with the Islamic republic, have been reluctant to back any more punitive measures.
A US national intelligence estimate released in early December reported that Iran abandoned its nuclear weapons programme in 2003.
The report's conclusion has significantly undermined US warnings about the Iranian threat.
Tehran said on Tuesday that it would not be swayed if new UN sanctions were imposed.
Gholam Hossein Elham, a government spokesman, said: "Adoption of a possible new resolution will not have any effect on our people."
After the head of the UN atomic watchdog agency visited Tehran in mid-January, Iran agreed to clear up all outstanding issues about its atomic drive within four weeks.
Diplomats now indicate that the grace period could stretch to six weeks.
Ivaylo Kalfin, Bulgaria's foreign minister, said on Tuesday after talks with his Iranian counterpart Manouchehr Mottaki that Tehran now appeared to be aiming for an accord by "the end of February or the beginning of March".