A UN Security Council deadline for Iran to halt uranium enrichment was set to expire on Thursday with no indication that Iran will comply.
In Washington, the US State Department said the Security Council should quickly move toward adopting international sanctions if Iran does not announce that it has suspended uranium enrichment and comes clean on its nuclear activities.
"We would expect that the parties would immediately begin formal discussions about a resolution that would call for sanctions," State Department spokesman Sean McCormack said on Wednesday.
The UN nuclear watchdog, the International Atomic Energy Agency (IAEA), was scheduled to report to the council on Thursday on Iran's nuclear activities, diplomats said. The Washington Post reported on Wednesday that the report will say that Iran has continued to enrich uranium.
Iranian President Mahmoud Ahmadinejad in recent public remarks has restated Iran's right to continue enriching uranium, which he insists is only for producing energy. The US and some of its allies suspect that Iran is using the programme to develop nuclear arms.
US Undersecretary of State Nicholas Burns will fly to Europe next week for a meeting of the political directors of permanent Security Council members and Germany, McCormack said.
A senior State Department official said the meeting was tentatively scheduled to take place on September 7 in Berlin, but added the German government was still trying to work out the logistics.
The five permanent members of the Security Council plus Germany have offered Iran incentives to come clean about its nuclear activities.
Iran has not accepted the proposal, offering last week only to enter into "serious negotiations," a response Washington said at the time "falls short" of the Security Council requirement.
The Security Council has so far announced no plans for formal discussion on a new resolution to punish Iran. The council has not scheduled a meeting for Thursday beyond receiving the IAEA report, said Ghanaian ambassador Nana Effah-Apenteng, whose country holds the rotating council presidency.
US ambassador John Bolton provided no immediate timeline for discussions on a new resolution that would include sanctions.
"If they have not (complied with the deadline), we will go to the UN to seek sanctions and it remains our intention to seek sanctions," Bolton said.
The US has pushed for sanctions on Iran, but Russia and China have opposed coming down too hard over business concerns and worries that harsh penalties will push Iran away from negotiations.