Iran began to enrich a second batch of uranium this week on the same day that world powers delivered a negotiating offer to Tehran conditioned on its suspension of nuclear activities, according to a report released Thursday by the International Atomic Energy Agency.

The timing of the nuclear work, which Western diplomats suggested was politically calculated, appeared to signal that Iran would fight to continue enriching uranium despite demands by the international community.

"On the timing, knowing the Iranians, nothing is left to chance," said a European diplomat, who requested anonymity.

In an offer delivered to Tehran on Tuesday by Javier Solana, the European Union's foreign policy chief, Iran would get a generous package of incentives--including trade and economic incentives and help building light-water reactors to provide electrical power--in exchange for giving up its enrichment work.

But Iran reintroduced uranium gas into its centrifuges on Tuesday and started to process a new batch of raw uranium, the IAEA report said.

There is no deadline for a response to the offer of incentives, but Western diplomats have said they expect Iran to answer in weeks, not months. Iranian President Mahmoud Ahmadinejad will meet next week with Chinese President Hu Jintao.

The report from the United Nations' nuclear watchdog, which was sent to the organization's 35-member board of governors before its meeting next week, contained "nothing earth-shaking," said a senior UN official. It outlined a long list of questions that Iran has not answered about its nuclear program, which was clandestine for 18 years until divulged by an Iranian opposition group.

However, the report disputed information from earlier this spring that suggested Iran had stopped its enrichment activities. According to the report, after an initial batch of uranium gas was fed into Iran's 164-centrifuge cascade in early April, scientists stopped feeding in the gas to all but two centrifuges.

But Iran continued to spin its 164-centrifuge cascade at Natanz, a key technological exercise.

By Alissa J. Rubin

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