Addressing the European Parliament's Foreign Affairs Committee, Solana said his talks with Iran had made some progress, but no agreement had been reached on the key issue of uranium enrichment.

"We have reached common ground on quite a number of subjects. But we haven't agreed on what is a key point: suspension (of uranium enrichment). So far, up to today, Iran has made no commitment to suspend," said Solana.

In its latest show of Iran's defiance, Iranian President Mahmoud Ahmadinejad vowed again on Wednesday that Tehran would not bow to the pressure of the West and halt its uranium enrichment-related activities.

"The Islamic Republic will not retreat one inch from its legal rights, and with glory, Iran will continue along its path," Ahmadinejad said in a speech outside the capital Tehran.

In another address delivered on the same day, the Iranian leader stressed that if Iran halted uranium enrichment there would be "nothing left to negotiate."

Enrichment of uranium is at the core of the dispute over Iran's nuclear program. The process can be used to make nuclear fuel and, in highly enriched form, the explosive core of an atomic bomb. Tehran insists its nuclear program is solely for peaceful energy needs.

The UN Security Council adopted a resolution in late July, urging Tehran to suspend, by Aug. 31, all enrichment-related and reprocessing activities, including research and development.

Solana said he had been engaged in talks with the Iranian authorities for four months with an aim to clarify whether a negotiation between Iran and six countries -- Britain, China, France, Germany, Russia and the United States -- could start on the basis of a June proposal.

The six countries offered Iran a package which included political, economic and nuclear technology incentives in return for Iran's suspension of uranium enrichment.

The six countries had followed a two-track approach: dialogue and referring the case to the UN Security Council, said Solana.

"Dialogue could not last forever. It is up to them (the six countries) to decide whether the time has come to follow the second track," he said. "But the door to negotiations is always open."

He said the issue "can only be solved, and will be solved, through negotiations."

Solana has previously said that negotiations with Iran could not start "formally" while enrichment was still in progress.

As the efforts to revive the negotiations continued to hit snags, the United States repeated its call for the Security Council to take action against Iran.

"The international community is running out of time because soon its own credibility in terms of enforcing its own resolutions will be ... a matter of question," said U.S. Secretary of State Condoleezza Rice.

French foreign ministry spokesman Jean-Baptiste Mattei said on Thursday that "If Iran does not conform to the obligations which follow from (Security Council) resolution 1696, the group of six will [decide on] the consequences."

Mattei added that if Iran continued to refuse to suspend its nuclear program, "The measures which could be taken under resolution 1696 should be progressive, proportionate and reversible."