"We reached a preliminary agreement at the experts level," a top negotiator, Hossein Moussavian, told state television by telephone from the French capital after what has been described as two days of "difficult discussions".

"This agreement is to be taken to the capitals of the four countries, and in the next days, if the capitals approve it, it will be announced officially," he said, adding that he was "not pessimistic".

"Should the four countries be able to agree on a package in the not-so distant future, there would be a crucial transformation in relations between Iran and the EU and the whole international community."

His announcement followed two days of talks between Iran and the EU troika of Britain, France and Germany on getting Tehran to suspend uranium enrichment in order to avoid being hauled before the UN Security Council for possible sanctions.

The United States accuses Iran of secretly trying to develop nuclear weapons under cover of its civilian atomic energy program and wants the UN nuclear watchdog, the International Atomic Energy Agency (IAEA), to refer Tehran to the Security Council when the agency meets in Vienna on November 25.

But veto-wielding Council members China and Russia -- which is helping Iran build its first nuclear power plant in a deal worth some 800 million dollars -- have voiced their opposition to the issue moving out of the IAEA.

Moussavian said the preliminary agreement included "a collection of political, economic, security, technological and trust-building cooperation regarding the future of Iran's peaceful nuclear activities".

But he refused to give any specific details pending its approval by "the most senior officials" in Iran as well as in the capitals of the EU's so-called "big three".

He also made no mention of whether Iran had agreed to meet EU demands that it halt its controversial work on the sensitive nuclear fuel cycle, activities that officials here insist are only aimed at producing fuel for civilian reactors.

The Europeans fear the process surrounding the enrichment of uranium could be eventually used by Iran to build a nuclear bomb.

Speaking to Iran's Arabic-language news channel al-Alam, Foreign Minister Kamal Kharazi said "there are still points that should be finalised" but added that "there is talk of continuing the suspension of enrichment for a short period of time until trust is built."

"We are ready to take steps to show our honesty and that there is no nuclear weapons plans in our military doctrine," Kharazi said. "The trend of the discussions were positive and we hope this continues."

According to Moussavian, the preliminary accord could get the green light as early as next week.

"After the four capitals have agreed, we will begin discussions on implementing this agreement. The next round of discussions will not be so challenging, because the principles will have been set," he said.

"I must emphasise that all this is pending the agreement of the four capitals. If it is not approved, we will have to say these discussions failed. But I am not pessimistic," he told state television.

According to diplomatic sources, Europe's three powers are believed to have offered Iran nuclear technology, including access to nuclear fuel, increased trade and help with Tehran's regional security concerns in exchange for a halt to enrichment.

The French foreign ministry has officially spoken of "considerable progress" but Western officials have not given any specific details.

Tehran has until now resisted Europe's demand for an indefinite suspension, arguing that it would infringe its right to maintain a civilian nuclear power programme. But a year ago Iran agreed to suspend enrichment -- albeit while continuing other fuel cycle work -- pending the completion of an IAEA probe.

Enrichment is permitted under the nuclear Non-Proliferation Treaty (NPT) -- the treaty overseen by the IAEA and to which Iran is a signatory -- if for peaceful purposes.

However Iranian officials have said they were open to maintaining a "voluntary" suspension -- but not a total halt -- of enrichment, a step the IAEA board called for in September.

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