"Possibly tomorrow," Gholamreza Aghazadeh told reporters Wednesday, when asked when Iran would sign the additional protocol to the nuclear Non-Proliferation Treaty (NPT).

Iran has been under international pressure to sign the text, amid suspicions it is using a civil atomic energy programme as a cover for secret nuclear weapons development.

Aghazadeh made no further comment, and it remained unclear who would sign the text on behalf of Iran at the International Atomic Energy Agency (IAEA) in Vienna.

Iran had been represented at the UN watchdog by nuclear expert Ali Akbar Salehi. He is due to be replaced by a diplomat, although a new permanent representative has yet to be officially named.

Last month, the IAEA condemned Iran for 18 years of covert nuclear activities, although a report said there was no clear evidence the country had been developing nuclear arms.

IAEA director Mohamed ElBaradei argues that the agency needs more powers as it continues to probe Iran, including the ability to carry out surprise inspections of suspect nuclear sites. Under the basic NPT, the IAEA is only authorised to carry out pre-arranged site inspections.

And Russia's Atomic Energy Minister Alexander Rumyantsev also warned Monday that Russia, under US pressure to stop its nuclear assistance to Iran, will not deliver nuclear fuel to Iran for its atomic power plant unless Tehran signs the additional protocol.

Moscow and Tehran are preparing an agreement under which Iran pledges to return all spent fuel from the nuclear reactor that Russia is building at Bushehr, in the south of the country.

Iran had been resisting the additional protocol, arguing that inspectors could violate national sovereignty and probe sites that are crucial to the defence of the country, lumped into an "axis of evil" by US President George W. Bush along with North Korea and the ousted regime in Iraq.

The country finally bowed to pressure after the IAEA threatened to refer its concerns to the UN Security Council, which would have left Iran vulnerable to sanctions.

That U-turn came in October during an unprecedented visit by the foreign ministers of the European Union's big three -- Britain, France and Germany. Iran agreed to sign the additional protocol, hand over full details of its activities and suspend uranium enrichment.

But pending the signing of the protocol, Iran had pledged to the IAEA that it would allow inspections within its terms.

Although the deal has been given the blessing of supreme leader Ayatollah Ali Khamenei, who has the final say on all matters of state, a number of influential conservatives have voiced their fierce opposition to allowing the tougher inspections.

Several had gone so far as to advocate following the path of fellow "axis of evil" member North Korea and pulling out of the NPT altogether.

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