WASHINGTON - Iran is making headway in building nuclear weapons, the Bush administration said Monday as Secretary of State Condoleezza Rice tried to iron out differences with Russia over a UN resolution designed to stop the program with economic sanctions.

Iran's President Mahmoud Ahmadinejad, casts his ballot for for the Assembly of Experts, a body of 86 senior clerics that is charged with monitoring Iran's supreme leader and choosing his successor, in Tehran on Friday, Dec. 15, 2006. [AP]

While not predicting when Iran would join the nuclear club, State Department spokesman Sean McCormack said the Iranians were trying to perfect technology to enrich uranium. Iran has denied an effort to build nuclear weapons and says its work is for energy development.

"It's a very tricky matter of perfecting centrifuge technology so you can actually enrich all the uranium," McCormack said. "So, yes, they are going along their way in trying to go down the various pathways."

The spokesman provided no details of Rice's telephone conversation with Russian Foreign Minister Sergey Lavrov. "They went over some of the outstanding issues," McCormack said.

Russia, which has close economic ties with Iran, has favored diplomacy over punitive sanctions, but the Bush administration is hoping Moscow may be prepared to approve a watered-down resolution at the UN Security Council.

"We are hopeful that we can get a vote in the very near future. It is time for a vote," McCormack said. "I think we need to see a vote on this in a matter of days."

The United States and its European allies have proposed offering Iran economic concessions in exchange for halting its enrichment of uranium, a key part of the process of building nuclear weapons.

US and other diplomats met Monday at the United Nations in an effort to narrow differences over a draft text.