Diplomats from the five permanent U.N. Security Council members and Germany plan to meet Tuesday in Moscow for talks on how to proceed with the Iran nuclear standoff.

The talks will set the stage for a formal Security Council meeting next week, when the United States is expected to press for language demanding that Tehran comply immediately with orders to stop enriching uranium. The enriched ore can power electrical plants or can be used to make nuclear bombs.

The United States accuses Tehran of using its nuclear program as a cover for developing an atomic bomb. Tehran insists its nuclear ambitions are peaceful.

Last week, Iranian President Mahmoud Ahmadinejad told Iranian students his government is testing a new centrifuge that can enrich uranium four times faster than older models. The Associated Press quotes a Vienna-based diplomat as saying International Atomic Energy Agency officials will discuss that claim with Iranian officials later this week.

On Sunday, a leading U.S. research organization posted satellite photography on its Web site purporting to show that Iran has reinforced a key underground uranium enrichment facility.

The imagery - published by the Institute for Science and International Security - said the pictures show the facilities at Natanz being buried under successive layers of earth and concrete.