Iran seems to have paused in developing its uranium enrichment program as it awaits U.N Security Council deliberations on harsher sanctions, the head of the International Atomic Energy Agency said Monday.

But IAEA chief Mohamed ElBaradei warned that lack of Iranian cooperation with agency inspectors meant it had not been able to establish that Tehran's nuclear activities served purely peaceful purposes.

And a senior Iranian official dashed hopes that any short-term pause could translate into Tehran accepting a U.N. Security Council demand to freeze its enrichment activities. Ali Ashgar Soltanieh, Iran's chief IAEA delegate, said his country would never give up its right to enrich.

Iran, the main issue at 35-nation IAEA board meeting that opened Monday, is not to formally come up until Tuesday at the earliest.

Still, ElBaradei touched on the dispute over Tehran's nuclear defiance both in his opening statement to the meeting and later comments to reporters.

"I do not believe that the number of centrifuges has increased, nor do I believe that nuclear material has been introduced to the centrifuges at Natanz," he said, referring to the machines used to enrich uranium at a site under IAEA monitoring.

But ElBaradei, whose agency has spent more than four years probing the nature of Tehran's nuclear activities, also said the IAEA remains "unable to provide the required assurance about the peaceful nature of Iran's nuclear program."

Unless Tehran takes "the long overdue decision" to cooperate with the IAEA, it "will have no option but to reserve its judgment about Iran's nuclear program, and as a result the international community will continue to express concern," he told reporters.

"Quite a few uncertainties still remain about experiments, procurements and other (nuclear) activities," he said, alluding to Iran's persistent refusal to meet agency requests for clarification about aspects of its nuclear program.

Soltanieh did not directly address the reported pause in enrichment activities. But he asserted that his country would "never give up its inalienable right" to develop enrichment -- which Tehran says it wants to develop to generate power but which also can produce the fissile material for nuclear warheads.

Diplomats familiar with the agency's Iran file said that Tehran continues to refuse IAEA requests to instal cameras that would give agency monitors a full view of its underground hall at Natanz, which Iran says will ultimately house 54,000 enriching centrifuges -- enough to produce dozens of nuclear weapons a year.

Growing fears that Tehran might be seeking to develop enrichment capabilities for its weapons applications led the U.N. Security Council late last year to impose sanctions on Tehran.

Lack of full remote monitoring means the agency cannot keep tabs on all activities at the bunker, said one diplomat, who demanded anonymity because he was not allowed to discuss the issue. Iran continues to assemble individual centrifuges in the hall, he said.

Up for review will be a Feb. 22 report from ElBaradei finding that Tehran has expanded enrichment.

The board was expected to approve last month's decision by ElBaradei to suspend nearly half the technical aid his agency provides to Iran. Only North Korea and Saddam Hussein's Iraq have faced such punishment in the past.

ElBaradei, in an internal report circulated to board members last month, had called for full or partial suspension of 18 projects that he deemed could be misused to create nuclear weapons. His agency had already suspended aid to Iran in five instances in January.

The board has often been split on what action to take against Iran. The United States, its key allies and most European nations have usually been opposed by nonaligned board members who were against harsh punishment.

But the diplomats said that even nations normally backing Tehran -- including key U.S. critics such as Cuba and Venezuela -- would likely agree to the suspensions because they were backed by the U.N. Security Council.

The board will also be reviewing North Korea's apparent willingness to ultimately dismantle its nuclear arms-making capabilities.

ElBaradei plans to go to Pyongyang March 13 as part of the six-nation agreement under which North Korea agreed to allow a return of his agency's experts after more than four years under its commitment to eventually scrap its nuclear program in exchange for economic aid and security assurances.