"Next week, we will get the letter by Iran for conclusion of the Additional Protocol, which is a positive step," International Atomic Energy Association (IAEA) chief Muhammad ElBaradei said on Saturday.
ElBaradei was talking to journalists after a 90 minute meeting with the head of Iran's Supreme National Security Council, Hasan Ruhani.
The IAEA chief also said Iran had promised him a letter next week formally announcing the "suspension of all enrichment-related activities."
"We have been getting satisfactory cooperation from Iran…I hope this is something that will continue," ElBaradei said when being asked if he considered Iran's cooperation to be adequate.
"Next week, we will get the letter by Iran for conclusion of the Additional Protocol, which is a positive step"
Iran's nuclear programme has been at the eye of a global storm since US President George Bush accused the country last year of seeking to clandestinely develop nuclear weapons.
Iran denies the charge, insisting its nuclear programme is for peaceful purposes.
On 21 October, Iranian officials told the foreign ministers of Germany, France and the United Kingdom that Tehran would not only sign the Additional Protocol permitting tougher inspections, but would temporarily stop enriching uranium.
"Iran will fulfil the content of the statement in Tehran which we agreed with the three ministers," Ruhani reiterated.