The United States and five other world powers are planning to demand what they call "unfettered access" to Iran's new nuclear facility.
A senior U.S. official, who refused to be named, says the United States and other world powers will also demand Iran turn over within weeks other information it has been withholding on its nuclear program.
Diplomats from the U.S. and the five other powers - Britain, France, Germany, Russia and China - are scheduled to meet with an Iranian delegation in Geneva Tuesday.
But even as world powers increase the pressure on Iran about its nuclear ambitions, Iran's president is refusing to back down.
President Mahmoud Ahmadinejad told reporters in Tehran Saturday that the U.S. and its allies already regret rebuking Iran over the facility's existence.
He also said the revelation of the second facility for enriching uranium struck a "blow" against Western powers.
The U.S., Britain and France accuse Iran of building the nuclear facility in secret - a charge Iran denies.
During his weekly address Saturday, U.S. President Barack Obama criticized Iran for a "disturbing pattern" of evasion, but said he is open to "meaningful dialogue."
Mr. Obama also told Tehran it must cooperate fully with the International Atomic Energy Agency and allow inspectors to visit the site near the Shi'ite holy city of Qom.
Iran's nuclear chief, Ali Akbar Salehi, told Iranian state television Saturday that inspectors will be allowed to visit.
A top aide to Iran's supreme leader said the uranium enrichment facility should be operational soon.
The United States and its allies accuse Iran of working to produce a nuclear weapon. Iran says its atomic program is for peaceful purposes, to generate electric power.
Some information for this report was provided by AFP, AP and Reuters.