WASHINGTON, April 8 (Reuters) - U.S. Secretary of State Condoleezza Rice on Tuesday called incentives offered to Iran in 2006 to curb its nuclear program "very generous" but would not say whether she was open to sweetening them.

Rice also told reporters she could not substantiate Iran's statement that it has begun installing 6,000 new centrifuges at its uranium enrichment plant and faulted Iran for not having accepted what she called a "reasonable" offer from major powers.

The U.N. Security Council has imposed three rounds of sanctions on Iran for defying council demands that it suspend its uranium enrichment program, which could be used to make fuel for power plants or atomic weapons.

In June 2006, the five permanent members of the U.N. Security Council and Germany held out incentives to Iran, including civil nuclear cooperation and wider trade in civil aircraft, energy, high technology and agriculture, if Tehran suspended uranium enrichment and negotiated with the six.

Senior diplomats from the group, which includes Britain, China, France, Germany, Russia and the United States, plan to meet in April to discuss whether to sweeten incentives, U.S. officials said on Monday.

Iran has refused to buckle to the sanctions and has spurned previous offers of economic benefits to suspend its uranium enrichment, which it says is to produce fuel for electrical power plants rather than for nuclear weapons.

Asked if the Bush administration was inclined to improve on the June 2006 offer, Rice replied: "The six parties have put forward, I think, a very generous set of incentives."

On Monday, a senior U.S. official made clear the United States' skepticism about improving on the offer but said it would hear out the others among the six who wished to do so.

Iranian President Mahmoud Ahmadinejad on Tuesday said Iran has begun installing 6,000 new centrifuges at its uranium enrichment plant, something Rice said she could not verify.

"I can't substantiate the claims -- and there are always multiple claims coming out of Iran about progress on this, or progress on that," Rice told a news conference with the foreign ministers of Canada and Mexico.

"I don't think that the underlying situation has changed, which is that Iran faces three separate Security Council (sanctions) resolutions.," she added. "Iran faces the continued isolation in the international community because it will not take a reasonable offer from the international community." (Reporting by Arshad Mohammed; Editing by David Wiessler)

AlertNet news is provided by