"We have seen a fairly slow development in commissioning new cascades," ElBaradei told reporters, referring to the installation of centrifuges which enrich uranium into fuel for civilian reactors or, in its highly refined state, atom bomb material. ElBaradei has called on Iran to freeze new enrichment work, holding it at current levels, in return for the United Nations holding off on new sanctions against Iran for its failure to heed UN Security Council calls for it to halt all enrichment work."

Iran has not yet frozen the work, ElBaradei said.

The Council has already imposed two rounds of sanctions.

ElBaradei has said he is seeking a "time-out" in the international confrontation fuelled by fears Iran is using its civilian atomic energy programme as a cover for the secret development of nuclear weapons.

Iran has so far said it will not halt or slow down its enrichment work.

ElBaradei said IAEA inspectors had noticed Iran's slowdown "in commissioning new cascades for the treatment of nuclear material" while on a visit to Natanz last week.

ElBaradei said he welcomed this since "Iran needs to do everything to cool things down."

There is a "need to shift from the mode of confrontation to the mode of goodwill and cooperation," ElBaradei said.

Meanwhile, the deputy head of the UN atomic watchdog visits Iran on Wednesday as the West turns up the pressure on Tehran to suspend its nuclear drive or face more sanctions.

Olli Heinonen, the International Atomic Energy Agency (IAEA) deputy director general for safeguards, will seek to shape a plan to resolve "outstanding issues" over Iran's nuclear ambitions.

Heinonen is making a two-day visit at the invitation of Iran's national security chief and top nuclear negotiator Ali Larijani, who met EU foreign policy chief Javier Solana last month over the standoff.

Britain and the United States have again warned the Islamic republic about its nuclear programme, which the West fears could be a cover for plans to build the bomb.

Britain said it will press for a third UN resolution to tighten sanctions on Iran if it continues to defy calls to suspend uranium enrichment, while US Secretary of State Condoleezza Rice has refused to rule out military action.