Washington has been trying to persuade Japan to drop its investment due to concerns over Tehran's nuclear programme, MEES said.

The Iranian oil ministry has "moved to divert international pressure on negotiations over the Azadegan oilfield development by inviting international companies ... to study data on the entire structure", said the Nicosia-based weekly.

"The National Iranian Oil Company has scheduled a meeting on September 16 in Tehran to hear from the invited companies whether they would like to take the talks further," it said.

"A handful of European and Asian companies have been formally invited by the (oil) ministry, in letters sent at the end of August," to study data on the whole Azadegan project, said MEES.

The newsletter said Tehran "believes the widening of the scope of the Azadegan discussion will reduce the pressure on Japan by increasing the numbers of countries which the US would need to win over."

Japanese Foreign Minister Yoriko Kawaguchi said last month that concerns over Iran's suspected nuclear programme would not influence negotiations with the Islamic republic on the multibillion-dollar oil deal.

But on Friday, the International Atomic Energy Agency imposed an October 31 deadline on Iran to prove it is not secretly developing atomic weapons, under a resolution co-sponsored by Japan.

Apart from its diplomatic support for Washington, the United States has demanded that Tokyo abandon the oil negotiations and warned of possible sanctions if the deal goes through.

Iranian government spokesman Abdollah Ramezanzadeh said in mid-July that "if the Japanese side does not want to go ahead, we will go to international tender", adding that Iranian officials had already "held talks with four or five other groups".

Japan and Iran agreed in 2000 to start negotiations over the field, but Iranian officials warned that a period of exclusive signing privileges for the Japanese consortium expired at the end of June and other companies could now be considered.

The Azadegan field, in southwest Iran, is considered to be the country's most important with estimated reserves of 26 billion barrels of oil.

Iranian President Mohammad Khatami gave Japan priority to develop the field during a visit to Tokyo in 2000.

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