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 maybe 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, according to the website of the official IRIB state broadcaster.

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, notably the European Union's announcement that it would ban all Iranian oil imports within the next five months, after weak economies such as Greece and Spain had found alternative suppliers.

Iran's parliament is considering a draft law that would pre-empt that EU ban by cutting off shipments to Europe immediately in a bid to destabilise the bloc. The bill could be debated on Sunday.

Iran, OPEC's second-biggest producer, has repeatedly brandished threats to use oil as a weapon if it is backed against the wall.

Political and military chiefs have warned they could even order the Strait of Hormuz, a chokepoint at the entrance to the Gulf, closed to all tanker traffic.

Such a move could send oil prices soaring by 50 percent, according to analysts, and tip the global economy into recession.

Saudi Arabia has promised to make up for any shortfall in the market should Iranian oil be curbed, but it, too, is dependent on passage through the strait.

The United States, which has called any attempt to close the strait a "red line" it would not tolerate, is reportedly planning to send a large floating base for commando teams to the Middle East.

It already has two aircraft carrier groups in and near the Gulf, and has broadened arms deals to Saudi Arabia and the United Arab Emirates.

Against that backdrop of threat and counter-threat, attention is focused on what the IAEA talks might yield.

It was not known, however, whether the delegation would be given access to Fordo or any of the other sites mentioned in a November IAEA report that stated strong suspicions that Iran had done work developing nuclear weapons.

IAEA chief Yukiya Amano on Friday, at the World Economic Forum in Davos, Switzerland, reiterated that his agency had "information that indicates that Iran has engaged in activities relevant to the development of a nuclear explosive device."

He called on Tehran to show "substantial cooperation" to the IAEA mission.

Iran has several times indicated that has been its position, but it has also alleged bias in the IAEA and kept the UN agency at arm's length.

Likewise, Iran has signalled willingness to resume talks with world powers Britain, China, France, Russia, the United States, and Germany that collapsed a year ago.

But thus far it has not replied to a letter sent three months ago by EU foreign policy chief Catherine Ashton offering a return to the talks, with emphasis on discussing Iran's nuclear activities.

That reply would be forthcoming "soon", Iranian Foreign Minister Ali Akbar Salehi said, according to the official news agency IRNA on Sunday.