Iran said on Sunday it was very optimistic over a visit by U.N. nuclear inspectors aimed at shedding light on suspected military aspects of Tehran's atomic work but suggested Tehran would curb cooperation if the experts became a "tool" for outside powers.
An International Atomic Energy Agency (IAEA) team began a three-day visit on Sunday to try to advance efforts to resolve a row about nuclear work which Iran says is for making electricity but the West suspects is aimed at seeking a nuclear weapon.
Tensions with the West rose this month when Washington and the European Union imposed the toughest sanctions yet in a drive to force Tehran to provide more information on its nuclear programme. The measures take direct aim at the ability of OPEC's second biggest oil exporter to sell its crude.
The Mehr news agency quoted Foreign Minister Ali Akbar Salehi as saying during a trip to Ethiopia: "We are very optimistic about the outcome of the IAEA delegation's visit to Iran ... Their questions will be answered during this visit,"
"We have nothing to hide and Iran has no clandestine (nuclear) activities."
Iran's parliament speaker, Ali Larijani, warned the IAEA team to carry out a "logical, professional and technical" job or suffer the consequences.
"This visit is a test for the IAEA. The route for further cooperation will be open if the team carries out its duties professionally," said , state media reported.
"Otherwise, if the IAEA turns into a tool (for major powers to pressure Iran), then Iran will have no choice but to consider a new framework in its ties with the agency."
Iran's parliament in the past has approved bills to oblige the government to review its level of cooperation with the IAEA. However, Iran's top officials have always underlined the importance of preserving ties with the watchdog body.
Before departing from Vienna, IAEA Deputy Director General Herman Nackaerts hoped for the Islamic state to tackle the watchdog's concerns "regarding the possible military dimensions of Iran's nuclear programme".
Less than one week after the EU's 27 member states agreed to stop importing crude from Iran from July 1, Iranian lawmakers were due to debate a bill later on Sunday that would cut off oil supplies to the EU in a matter of days.
Some parliamentarians told Reuters that the debate might be postponed to Wednesday.
By turning the sanctions back on the EU, lawmakers hope to deny the bloc a six-month window it had planned to give those of its members most dependent on Iranian oil - including some of the most economically fragile in southern Europe - to adapt.
The head of the state-run National Iranian Oil Company (NIOC) said late on Saturday that the export embargo would hit European refiners, such as Italy's Eni, that are owed oil from Iran as part of long-standing buy-back contracts under which they take payment for past oilfield projects in crude.
"The decision must be made at high echelons of power and we at the NIOC will act as the executioner of the policies of the government," Ahmad Qalebani told the ISNA news agency.
"The European companies will have to abide by the provisions of the buyback contracts," he said. "If they act otherwise, they will be the parties to incur the relevant losses and will subject the repatriation of their capital to problems."
"Generally, the parties to incur damage from the EU's recent decision will be European companies with pending contracts with Iran."
Italy's Eni is owed $1.4-1.5 billion in oil for contracts it executed in Iran in 2000 and 2001 and has been assured by EU policymakers its buyback contracts will not be part of the European embargo, but the prospect of Iran acting first may put that into doubt.
Eni declined to comment on Saturday.
The EU accounted for 25 percent of Iranian crude oil sales in the third quarter of 2011. However, analysts say the global oil market will not be overly disrupted if parliament votes for the bill that would turn off the oil tap for Europe.
"The Saudis have made it clear that they'll step in to fill the void," said Robert Smith, a consultant at Facts Global Energy.
"It would not pose any serious threat to oil market stability. Meanwhile Asians, predominantly the Chinese and Indians, stand to benefit from more Iranian crude flowing east and at potential discounts."
Potentially more disruptive to the world oil market and global security is the risk of Iran's standoff with the West escalating into military conflict.
Iran has repeatedly said it could close the vital Strait of Hormuz shipping lane if sanctions succeed in preventing it from exporting crude, a move Washington said it would not tolerate.
The IAEA's visit may be an opportunity to defuse some of the tension. Director General Yukiya Amano has called on Iran to show a "constructive spirit" and Tehran has said it is willing to discuss "any issues" of interest to the U.N. agency, including the military-linked concerns.
But Western diplomats, who have often accused Iran of using such offers of dialogue as a stalling tactic while it presses ahead with its nuclear programme, say they doubt Tehran will show the kind of concrete cooperation the IAEA wants.
They say Iran may offer limited concessions and transparency to try to ease intensifying international pressure, but that this is unlikely to amount to the full cooperation required.
The outcome could determine whether Iran will face further international isolation or whether there are prospects for resuming wider talks between Tehran and the major powers on the nuclear dispute.
Salehi said Iran "soon" would write a letter to the E.U.'s foreign policy chief Catherine Ashton to discuss "a date and venue" for fresh nuclear talks.
"Iran's top nuclear negotiator Saeed Jalili in this letter, which may be sent in the coming days, also may mention other issues as well," Salehi said, without elaborating.
The last round of talks in January 2011 between Jalili and Ashton, who represents major powers, failed over Iran's refusal to halt its sensitive nuclear work.
"The talks will be successful as the other party seems interested in finding a way out of this deadlock," Salehi said.