Tehran: IAEA officials began a three-day visit to Iran on Sunday to discuss the Islamic republic's suspect nuclear programme, amid a backlash by furious Iranian lawmakers at a looming EU oil embargo.

The International Atomic Energy Agency mission is to address evidence suggesting Iran's activities include research for a nuclear weapon.

The visit was seen as a rare opportunity to alleviate a building international showdown over Iran's nuclear programme that has seen a ratcheting up of sanctions and talk of possible military action by Israel.

"In particular we hope that Iran will engage with us on the possible military dimensions of Iran's nuclear programme," Herman Nackaerts, the IAEA's chief inspector leading the delegation, told reporters in Vienna as he left.

"We are looking forward to the start of a dialogue, a dialogue that is overdue since very long," he said.

Iran's parliamentary speaker Ali Larijani on Sunday called the visit a "test" for the UN agency.

If the IAEA officials were "professional" then "the path for cooperation will open up," Larijani said.

"But if they deviate and become a tool, then the Islamic republic will be forced to reflect and consider a new framework" for cooperation, he added.

Iran, which maintains its programme is exclusively for peaceful purposes, is increasingly furious at the Western measures being levelled at its economy to get it to halt uranium enrichment.

It has defiantly stepped up the enrichment at a new bomb-proof bunker in Fordo, near the Shiite holy city of Qom. It is also reacted fiercely to new sanctions targeting its oil and finance sectors.