Ambassador John Sawers spoke before heading into a high-level meeting at U.N. headquarters of nations concerned with events in Pakistan.
After the meeting, British Foreign Secretary David Miliband said the resolution will be introduced in the Security Council on Friday.
Western diplomats said the resolution would reaffirm three rounds of earlier U.N. sanctions to make clear that the process has not been dropped and that the council wants Iran to comply.
The diplomats spoke on condition of anonymity because details have not been made public.
The United States, Britain and France have been pressing for a new round of sanctions to step up pressure against Iran for its continuing refusal to suspend uranium enrichment as a prelude to talks on its nuclear program. But Russia and China objected to new sanctions.
The proposed new resolution appears to be a compromise - no new sanctions but a tough statement to Iran that Security Council resolutions are legally binding and must be carried out.
Russia on Tuesday scuttled high-level talks on imposing new sanctions on Iran that had been set for Thursday between the foreign ministers of the five permanent members of the U.N. Security Council and Germany, the key players in seeking an agreement with Iran. Even sanctions opponent China had agreed to the meeting.
U.S. officials, including Secretary of State Condoleezza Rice, sought to downplay the move, saying the time wasn't right for the session. But they had previously said such a gathering would be useful and necessary to get a fourth Security Council sanctions resolution on Iran.
Iran insists its nuclear program is purely peaceful and designed to produce nuclear energy, but the U.S. and Europeans suspect Tehran is pursuing nuclear weapons.
Iranian President Mahmoud Ahmadinejad said Thursday that Tehran needs the ability to produce nuclear fuel because it cannot rely on other nations to supply enriched uranium to the Islamic regime's planned reactors.