The U.N. nuclear watchdog on Monday confirmed plans for a January 29-31 visit to Iran and said its main objective was to resolve all outstanding substantive issues, referring to suspicions of military dimensions to the Iranian atomic energy programme.

A senior International Atomic Energy Agency team is expected to seek explanations during the talks in Tehran for intelligence information indicating that Iran has pursued research and development relevant to nuclear weapons, diplomats say.

The IAEA mission will be led by Deputy Director General Herman Nackaerts, head of nuclear safeguards inspections worldwide, and will include Rafael Grossi, the assistant director general for policy.

The Agency team is going to Iran in a constructive spirit, and we trust that Iran will work with us in that same spirit, Yukiya Amano, Director General of the Vienna-based agency, said in a statement.

The overall objective of the IAEA is to resolve all outstanding substantive issues, the IAEA statement added, confirming for the first time the dates for the visit.

Iran's ambassador to the IAEA told Reuters last week the visit would take place from January 29-31 and that his country was open to discuss any issues of interest for the U.N. agency.

But Western diplomats, who have often accused Iran of using stalling tactics in the long-running nuclear dispute while it presses ahead with its atomic activities, are sceptical about the chances for major progress in the talks.

Tension between Iran and the West has increased since November, when the IAEA published a report that said Tehran appeared to have worked on designing a nuclear weapon.

Iran, one of the world's leading oil producers, says its nuclear energy program is peaceful and aimed at generating electricity.

(Reporting by Fredrik Dahl; editing by Mark Heinrich)