TEHRAN (Reuters) - Iran and the U.N. atomic watchdog began talks on Monday on the Islamic state's disputed nuclear program, which the West fears is a front to build weapons, the official IRNA news agency reported.

IRNA said Hermann Naeckerts from the International Atomic Energy Agency (IAEA) met Ali Asghar Soltanieh, Iran's representative at the IAEA, behind closed doors.

"The talks, which will last for three days, are at the level of experts," IRNA quoted an unidentified official as saying.

"Experts from Iranian Foreign Ministry also are presented at the meeting."

Soltanieh and the IAEA's top investigator Olli Heinonen held two round of talks in Tehran last month on intelligence that Iran researched how to make nuclear bombs.

Iran says such talks are intended to advance cooperation between Iran and the IAEA.

The IAEA said in April Tehran had agreed on steps to clarify the intelligence reports by the end of May. Iran says the intelligence is fabricated.

The intelligence came variously from a laptop computer given to Washington by an Iranian defector in 2004, from other Western countries and from the IAEA's own inquiries.

The world's fourth-largest oil producer says its nuclear program is aimed at generating electricity so that it can export more oil and gas.

Major powers are expected to offer a revised package of trade and other incentives to Iran in the next few days if Tehran suspends its sensitive nuclear work.

Tehran has so far refused to do so and has said it will not consider any incentives that violate its right to nuclear technology.

It says it has prepared its own ideas to help end the dispute with the West over its nuclear ambitions, which has prompted three rounds of U.N. sanctions against Tehran since 2006.

Iran's President Mahmoud Ahmadinejad will unveil details of Iran's package at a news conference on Tuesday, a senior official told Reuters.

(Writing by Parisa Hafezi; editing by editing by Andrew Dobbie)

---