The UN secretary general has said he doubts the UN's nuclear watchdog will be able to decide next month whether to refer Iran to the UN Security Council.
Mr Annan said the IAEA might have to wait until March to refer Iran
Kofi Annan said the International Atomic Energy Agency's report on Iran's nuclear programme would probably not be ready on time for the meeting.
Earlier, Iran warned it would begin enriching uranium if it was referred to the Security Council for sanctions.
Iran insists its programme is solely aimed at meeting its energy needs.
However, Western countries suspect that Tehran may be seeking to develop nuclear arms.
Foreign ministers of the five permanent members of the Security Council plus Germany will meet in London early next week to discuss their strategy on Iran ahead of an emergency meeting of the IAEA in Vienna on 2 February.
Speaking at the World Economic Forum in the Swiss ski resort of Davos, Mr Annan said IAEA members might have to wait until March to discuss the report on Iran's nuclear activities.
"I am not sure that they will be ready to refer [Iran] to the Security Council if the official report of the board has not been released and deliberated upon by the board and a decision taken," he told Reuters news agency.
IRAN'S NUCLEAR STANDOFF
Sept 2002: Work begins on Iran's first reactor at Bushehr
Dec 2002: Satellites reveal Arak and Natanz sites, triggering IAEA inspections
Nov 2003: Iran suspends uranium enrichment and allows tougher inspections
June 2004: IAEA rebukes Iran for not fully co-operating
Nov 2004: Iran suspends enrichment under deal with EU
Aug 2005: Iran rejects EU plan and re-opens Isfahan plant
Jan 2006: Iran re-opens Natanz facility
Though mindful of Iran's warning, Mr Annan said he was encouraged that Tehran's top nuclear negotiator, Ali Larijani, was "positive" about a proposal to enrich uranium in Russia as a way to ease international concerns.
"As you know, I have appealed to the Iranians not to escalate, maintain the situation as it is today in order to create the right environment and confidence that negotiations are serious and lead to concrete results that would be mutually acceptable," Mr Annan said.
"It is also encouraging to hear the Iranians say they are considering the Russian offer very seriously. It is a solution that the international community is ready to accept."
BBC world affairs correspondent Jonathan Charles says Mr Annan's comments will not please those who believe that Iran's decision to restart nuclear research is unacceptable and are urging that Iran be referred to the Security Council for censure.
There are many at the UN who do not want the West to dictate the timetable and this may be the reason why they are trying to prevent the Iran report being brought forward, our correspondent says.