VIENNA - The UN nuclear watch dog and Iran reached a preliminary agreement on structured approach at the meeting in Tehran last Thursday over Iran's disputed nuclear activities, diplomats said on Thursday.

Both International Atomic Energy Agency (IAEA) and Iran announced progress was made in Thursday's talk towards an agreement the IAEA believes would allow the agency to resume inquiry into the nuclear facilities in Iran.

A Vienna-based diplomat told Xinhua that the preliminary consensus on structured approach between two sides is considered as the precondition of the new round of talk and also makes the agency more confident to achieve a breakthrough with Tehran, though Iran didn't agree to open access to the Parchin military base near Tehran for the UN inspectors in the talk last week.  .

The IAEA told the member states in a note that it looked forward to finalize the framework in the new round of discussions in Tehran on January 16, and start implementing it soon.

However, for both sides, Parchin issue would be the key barrier in the tough talks, as Iran requests the site should be closed since the questions had been addressed, and remain "a history of investigation."

On the other side, Herman Nackaerts, the agency's chief inspector said, "access to Parchin is part of the structured approach," and he expected to implement it after agreeing on the approach shortly, suggesting Parchin remains the agency's fist agenda in the agreement.

Iran said it has no interests in developing nuclear weapon, and its nuclear activities is for peaceful purpose, while the western states suspect Iran is heading for a nuclear bomb.

The IAEA urges Iran to open access to Parchin, saying Tehran might have conducted explosive experiment which is suspected to link to Iran's nuclear program, and suggests Iran is now removing those evidence.