"We will very probably give our response by tonight," senior Iranian diplomat and nuclear negotiator Hossein Moussavian told AFP as a deadline for an answer loomed.

"There are still internal discussions at a high level," he said, adding "it is not yet clear" if the Islamic republic's clerical leadership would approve or reject a tentative agreement reached last weekend in Paris with the three European Union states.

And foreign ministry spokesman Hamid Reza Asefi told state television that "it is imperative that our response takes into account our national interests."

The Europeans are pushing for Iran to accept a suspension of its work on the nuclear fuel cycle, including the enrichment of uranium, to ease international alarm over what the United States alleges is a covert weapons drive.

In return, Europe's three major powers are offering Iran civilian nuclear technology, including access to nuclear fuel, increased trade and help with Tehran's regional security concerns.

The International Atomic Energy Agency (IAEA), which has been probing Iran for nearly two years, has told the country it must respond this week in writing to the European deal if it wants its position included in a report for an IAEA meeting in Vienna on November 25.

"The IAEA is under the obligation to issue its report in a time frame pretty much two weeks before the board meeting," a Vienna-based diplomat said. Thursday marks the two-week deadline before the meeting.

This meeting will decide whether to take the Iranian dossier to the UN Security Council for possible sanctions, something Washington has been pushing for.

Iran asserts it is only interested in generating electricity and has frequently complained of being the victim of "double standards" given that Israel -- believed to be the Middle East's sole nuclear-armed state -- is not under any international pressure.

But despite Iran's delay in responding, Moussavian denied reports from the IAEA in Vienna of a snag in the diplomacy and that Tehran had asked for more concessions than the two sides had worked out in Paris last week.

"This is not correct. The last agreement is the Paris agreement. We are supposed to say yes or no to the whole package," he said.

The main sticking points in the tentative agreement on getting Tehran to suspend uranium enrichment are over the length and extent of any halt, diplomats said.

Iran has agreed to suspend the making of the uranium hexafluoride gasthat is the actual feed for the enrichment process but appears unwilling to suspend other stages in the fuel cycle.

Uranium conversion makes the uranium gas needed for the enrichment process which makes nuclear fuel, but which can also be the raw material for atomic bombs.

The 25-nation EU, led by Britain, France and Germany, says Iran must indefinitely and fully suspend uranium enrichment activities, but Iran insists its right to enrichment -- permitted under the nuclear Non-Proliferation Treaty (NPT) if for peaceful purposes -- cannot be called into question.

On Wednesday, former president and top regime cleric Akbar Hashemi Rafsanjani said Iran was at a "crucial point" in its stand-off with the UN atomic watchdog, while another official warned Iran could continue pursuing its nuclear drive "underground" and quit the NPT that empowers the IAEA if it came under too much pressure.

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