Washington ? The U.S. and its five allies trying to stop Iran’s suspected nuclear weapons program plan to tell Tehran in a key meeting on Thursday that it must provide “unfettered access” to its previously secret Qom enrichment facility within weeks, a senior administration official says.

The allies — the U.S., Britain, France, Germany, China and Russia — also will present in the Oct. 1 meeting a so-called transparency package covering all of Iran’s nuclear activities across the country, the official said. The official spoke on condition of anonymity in order to discuss plans that are not yet ready to be announced.

The allies will demand that Iran prove to the increasingly skeptical group that its intentions with its various sites are peaceful and energy-related, as Iran claims, and not for weapons development, as the West believes, the official said Saturday.

These nations now agree that they are less inclined to listen to suspect arguments or incomplete evidence — viewing it as a stall tactic, the official said.

But beyond the timeframe of “weeks” for coming clean on Qom, the allies will not give Iran a specific deadline to provide the information about its overall program, the official said.

The development of such a timeframe will depend on the Iranians’ actions in the meeting and directly after it, the official said.

The kind of transparency the group wants from Tehran is far-reaching, covering people, timeframes and facilities. This would include full access for the International Atomic Energy Agency to any and every site, notebooks, computers and documents related to nuclear development, and all scientists.

The United States will be represented in Thursday’s meeting in Geneva by William Burns, the under secretary of state for political affairs, a career diplomat.

On Saturday, Iran’s nuclear chief told state TV that his country would allow the U.N. nuclear agency to inspect Iran’s newly revealed and still unfinished uranium enrichment facility. Ali Akbar Salehi didn’t specify when inspectors from the IAEA could visit. He said the timing would be worked out with the U.N. watchdog.

Earlier Saturday, President Barack Obama offered Iran “a serious, meaningful dialogue” over its disputed nuclear program, while warning Tehran of grave consequences from a united global front.

“Iran’s leaders must now choose — they can live up to their responsibilities and achieve integration with the community of nations. Or they will face increased pressure and isolation, and deny opportunity to their own people,” Obama said in his radio and Internet address Saturday.

The White House responded to the development by urging Iran’s complete and immediate cooperation with the IAEA. “After hiding this site from the international community for years, full transparency is essential, and it is time for Iran to play by the rules like everyone else,” White House spokesman Tommy Vietor said.

Obama said in his address that evidence of Iran’s building the underground plant “continues a disturbing pattern of Iranian evasion” that jeopardizes global nonproliferation.

Evidence of the clandestine facility was presented Friday by Obama and the leaders of Britain and France at the G-20 economic summit in Pittsburgh. The news overshadowed developments on regulating financial markets and reducing fossil fuel subsidies.

At a news conference in New York, Iranian President Mahmoud Ahmadinejad said his country had done nothing wrong and Obama would regret his actions.