The meeting, proposed for international talks in Kazakhstan Tuesday to resolve disputes about Iran's nuclear program, would accelerate nuclear diplomacy ahead of Iran's presidential elections in June, U.S. officials told The Wall Street Journal.
But U.S. diplomats said they doubted Tehran would accept the offer because Ayatollah Ali Khamenei, Iran's supreme leader and chief arbiter on foreign relations, has ruled out direct talks with Washington.
"They say, 'Let us negotiate to force Iran to accept what we tell them,'" Khamenei said Sunday in a Tehran speech. "Such talks would be worthless. Such talks will lead nowhere."
But ahead of Iran's June 14 presidential and local council elections, U.S. and European officials told the Journal it was possible the offer would split Iran's political elite and perhaps isolate Khamenei.
If Tehran turns down the U.S. offer, Khamenei may feel increased pressure inside Iran and internationally if he is seen as the chief obstacle to diplomatic progress on Iran's nuclear program, Obama administration and European officials told the Journal.
"If Iran says yes, that would be great," said a European diplomat working on Iran. "If not, we think they'll be more isolated."
The international talks with Iran in Almaty, Kazakhstan's commercial and cultural hub, are to include the five permanent members of the U.N. Security Council, plus Germany, a group known as the P5-plus-1.
Washington plans to make the invitation through the office of Catherine Ashton, the EU foreign policy chief, who leads the P5-plus-1 team, the Journal said.
The meeting will be the first focused on Iran's nuclear program since June.
At the meeting, Britain, China, France, Russia, the United States and Germany plan to make "a substantial and serious offer" to Iran containing "significant new elements," a Western diplomat told reporters Wednesday, offering no further details.
U.N. nuclear watchdog the International Atomic Energy Agency reported Thursday Iran installed nearly 200 fast centrifuge machines at its main uranium-enrichment facility.
The 200 centrifuges -- which spin three to five times faster than the current IR-1 model -- are part of 3,000 advanced centrifuges Iran said it planned to add to the million-square-foot uranium-enrichment plant, near a major highway 20 miles northwest of the central Iranian town of Natanz.
The report can be found at tinyurl.com/Natanz-Nuclear.
In January Iran told the IAEA it planned to install the new machines. That prompted warnings from Western governments.
The White House said Jan. 31 the plan was "a further escalation and a continuing violation" of U.N. resolutions on the issue and "yet another provocative step by Iran."
The State Department offered the same message Thursday.
"The fact remains that the installation of new advanced centrifuges would be a further escalation and a continuing violation of Iran's obligations under the relevant U.N. Security Council resolutions and IAEA board resolutions," State Department spokeswoman Victoria Nuland told reporters. "So it would mark yet another provocative step."
Nuland said Tuesday's talks would give Iran an opportunity "to be serious ... [and] to allay the international community's concerns -- and we hope they take that opportunity."
Iran insists it is legally entitled to enrich uranium for peaceful purposes and denies it wants to become a nuclear weapons state.