"There will be another conference call among the P5 plus one tomorrow morning," State Department spokesman Tom Casey told reporters. "And I'm sure we'll have an opportunity to discuss the elements of this next resolution."

The United States has been involved in protracted negotiations with Russia, China, Britain and France -- the five permanent UN Security Council members, or P5, that all have veto power -- and Germany.

The so-called two-track strategy aims at offering Iran a dialogue that could give it economic benefits if it stops enriching uranium, or at threatening a third round of punitive sanctions.

The political directors of the US State Department and foreign ministries of the five other countries held a 90-minute conference call on December 11 about Iran's nuclear program, but did not finalize a draft sanctions resolution.

Secretary of State Condoleezza Rice admitted afterward that the United States has "tactical differences" with Russia and China about the "timing, about the nature of any further sanctions."

But she said that "the two-track strategy remains in place," when asked if the National Intelligence Estimate, published December 3, undercut the US drive for sanctions.

The report said Iran had stopped an alleged nuclear weapons program in 2003. Iran insists its nuclear program is peaceful.

Casey said he was not aware that the Russian government had linked its nuclear fuel deliveries to Iran's first atomic power station, which Washington does not object to.

"UN Security Council resolutions specifically exempted the Bushehr facility from other sanctions related to Iran's nuclear program," Casey said.

Enriched uranium is needed for nuclear power stations, but can, with further enrichment, be turned into weapons-making material. Iran has defied two rounds of UN sanctions aimed at forcing it to halt such sensitive work.

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