"June 29 (when G8 foreign ministers are to meet in Moscow) is more or less a deadline," a senior European diplomat said.

The diplomat said Solana had given the Iranians this unofficial deadline when he presented them with a package of possible trade, security and technology benefits, on behalf of Britain, China, France, Germany, Russia and the United States on June 6 in Tehran.

"Solana said that. That this was the deadline," for answering the world powers proposal, the diplomat said.

The eventual talks would call for guarantees that Iran would not seek to develop nuclear weapons.

A second diplomat, who like the first asked not to named due to the extreme sensibility of the consultations, stressed that the timing remained flexible, as the goal was to get a positive response from Iran.

"If they ask for a little bit more time, I'm sure that we will give it to them," the diplomat said.

But US President George W. Bush has said Iran had "weeks, not months" to agree to a freeze of uranium enrichment, which makes fuel for nuclear power reactors but can also be used to manufacture the explosive core of atom bombs.

Bush on Monday warned Iran of "progressively stronger political and economic sanctions" if Tehran refuses to freeze sensitive nuclear activities in return for talks.

Iran has however ruled out suspending enrichment and has said it will come up with a counter-offer, but Bush said Tehran's halting nuclear fuel work is a non-negotiable condition for moving forward on ending the crisis.

A third diplomat said: "If I were the Iranians, I would give them the answer on July 1. In negotiations, you do not accept such time limits."

But the Western diplomat said: "We're anticipating a reply before the June 29 meeting."

The diplomats said Solana was trying to arrange a meeting with Iran's top nuclear negotiator Ali Larijani before then.

A diplomat close to the consultations said a meeting between the two for last week was called off because Larijani was reportedly too ill to travel.

But the two men talked by telephone, the diplomat said.

"We're expecting a partial answer without a full suspension," a Western diplomat said, adding that this "won't be good enough."

The European diplomat said the timing of diplomacy would depend "on what kind of an answer the Iranians give, how much of a door they leave open."

Iran has insisted that it was not given any deadline.

Tehran says its nuclear program is a peaceful one to generate electricity, but Washington and the European Union fear it is a cover to develop atomic weapons. They are threatening UN Security Council sanctions if Iran does not cooperate.

The G8 foreign ministers will be preparing a G8 summit in St. Petersburg, Russia, to be held from July 15-17.

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