"We are soon going to send a letter indicating our intention and our readiness to accede to the protocol," said Iran's representative to the IAEA, Ali Akbar Salehi.
"A letter has been drafted. It has been given to officials. They are studying it," he added, explaining that the final say was now up to Hassan Rowhani, the secretary of Iran's Supreme Council of National Security.
Iran pledged to sign the protocol during a visit to Tehran on October 21 by the foreign ministers of Britain, France and Germany that extracted a series of concessions from the Islamic republic over its nuclear programme.
Salehi said he expected a decision to be made and the IAEA to be informed in the coming days -- well ahead of the IAEA's next board of governors' meeting on November 20.
"It's a matter of days," he said, adding that Iran has attached "no conditions" to its signature.
As a signatory to the NPT, Iran is currently only subject to pre-arranged IAEA inspection visits. But pending the signature and ratification of the protocol, it has pledged to work within the terms of the accord and allow unlimited inspections.
"It will be distributed and tabled to the board. The board has to endorse it and authorise the (IAEA) director general (Mohamed ElBaradei) to go into the process of signature with the Islamic Republic of Iran," he explained.
Salehi also said Iran was currently working through the modalities of suspending uranium enrichment -- a key IAEA demand which Iran's clerical leaders agreed to meet during the visit by Britain's Jack Straw, Dominique de Villepin of France and Germany's Joschka Fischer.
"It is being worked on. Suspension needs some procedures to be worked out," he said, adding that a halt to Iran's work on the nuclear fuel cycle was "probably a matter of weeks, maybe before or after the (next IAEA) board meeting".
He also confirmed that he was currently engaged in discussions with a team of visiting IAEA experts, whose work, he said, consisted of "making interviews, discussions, visiting of sites".
The team is expected to remain here until October 31, the expiry of an IAEA deadline for Iran to come clean on its nuclear activities.
The United States accuses Iran of using a nuclear power programme as a cover for developing nuclear weapons.
During the unprecedented visit by the European Union's big three foreign ministers, Iran also agreed to make a full declaration of its activities, and on Thursday handed the IAEA a report with information about its controversial nuclear programme.
Salehi reiterated that Iran had given "complete information", but acknowledged "some more explanation" might be required by the IAEA.
He said questions were likely to be posed over Iran's purchase of nuclear equipment "through intermediaries on the unofficial market".
"It goes back 16, 15 years. But since they're experts, they certainly can trace these," he said of the IAEA.
Iran was asked to cease uranium enrichment after IAEA inspectors found traces of highly enriched uranium during previous visits.
Iran says the traces came into the country on imported equipment, but has been resisting providing details of its trading, apparently to protect sensitive information on its import sources.