Iran's top nuclear negotiator Ali Larijani and EU foreign policy chief Javier Solana had been due to meet on Thursday, possibly in Spain, for their second encounter in just over a month.

However Iran's foreign ministry spokesman Mohammad Ali Hosseini unexpectedly told reporters at his morning press briefing the meeting had been postponed to allow both sides more time.

"For the Larijani-Solana meeting, no date or venue has been set. With the agreement of both sides it has been postponed," he said.

However amid confusion and concern over why the key meeting had been so suddenly shelved, the foreign ministry later issued a statement from Hosseini's office saying that the talks would, as planned, be held on Thursday.

It also indicated that the two men had been in touch recently to confirm the date but did not say if this was after the announcement of the postponement at 0700 GMT Sunday.

"In the light of the latest agreement between Mr Larijani and Mr Solana, the date for the negotiations is Thursday, May 31," said the statement.

"The venue will be decided through their contacts," it added. There was no explanation for the morning's announcement.

The meetings between Larijani and Solana are central to diplomatic efforts to resolve the standoff, which has already seen Iran slapped with two sets of UN sanctions for its refusal to suspend uranium enrichment.

After missing the latest UN Security Council deadline to suspend the process, Western powers are now pressing for Iran to face further penalties for its defiance.

Even when the pair meet, it remains unclear whether the two sides will be able to achieve any breakthrough, with the EU wanting Iran to freeze uranium enrichment and Tehran refusing to even consider such a move.

Iran's right to enrichment is the main obstacle toward resolving the standoff as the sensitive process can be used both to make nuclear fuel and, in highly extended form, to produce the fissile core of an atomic bomb.

The United States accuses Iran of seeking nuclear weapons, a charge vehemently denied by Tehran, which says it just wants to produce energy for a growing population whose fossil fuels will eventually run out.

Washington has never ruled out the use of force to resolve the standoff and has sent a clear warning to Iran by sailing two nuclear-powered aircraft carriers through the Straits of Hormuz.

Hosseini however brushed off the move. "The US military build-up in the Persian Gulf is aimed mostly at lifting their spirits," he commented.

The Larijani-Solana talks are due just three days after eagerly awaited talks in Baghdad on Monday between Iran and its arch enemy the United States.

The talks between US ambassador to Iraq Ryan Crocker and Iranian ambassador Hassan Kazemi will be the highest-level public talks involving only envoys of the two sides since the 1979 Islamic revolution.

However both sides have insisted that the talks be strictly limited to Iraq, with no chance of the discussions straying into the nuclear crisis.

In a sign of the tension that still exists between the two foes, Iran's intelligence minister said on Saturday that the Islamic republic had smashed several spy networks run by the US-led coalition in Iraq.

"Several espionage networks linked to the occupation forces in Iraq have been identified and dismantled in the west, southwest and central regions of Iran," said Gholam Hossein Mohseni Ejeie, without elaborating.

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