Iran's foreign minister will meet with the United States and other Security Council members on Thursday, diplomats said, as Tehran faces the possibility of new U.N. sanctions over its nuclear program.

"The Iranian mission is hosting all members of the Security Council this evening," a U.N. diplomat told Reuters on condition of anonymity. "All countries will be represented."

Several diplomats said that the U.N. ambassadors of the United States, Britain and France would not be attending the dinner with Foreign Minister Manouchehr Mottaki organized by Iran's U.N. mission, but would be sending deputies instead.

Another council diplomat said the majority of the other 12 council members would be sending their ambassadors to the dinner, which will take place at the Iranian ambassador's residence. It was not immediately clear when a U.S. diplomat last attended a dinner or reception hosted by Iran.

Washington does not have formal diplomatic relations with Iran and rarely participates in meetings with Iranian officials outside of the United Nations.

"We see this as an opportunity for Iran to show the council that they're prepared to play by the rules and meet their obligations," a U.S. official said, explaining why Washington would participate in Thursday's meeting.

"Iran has been offered many opportunities to prove the peaceful nature of its nuclear program," the official added.

"This meeting is another indication of the lengths the Iranians are going to make their case," he said. "They clearly recognize that the ongoing efforts in the Security Council and elsewhere are isolating them and doing them harm."

Another Western diplomat on the council said the meeting proved the council was continuing to pursue a "dual-track approach" with Iran -- negotiations combined with the threat of sanctions.

"We want to keep talking," the diplomat said.

Washington and its Western allies suspect Iran of developing nuclear weapons under cover of a civilian atomic energy program.

Tehran insists that its nuclear ambitions are limited to the peaceful generation of electricity, but has refused to halt sensitive activities that could enable it to develop weapons.

The United States, Britain, France, Russia, China and Germany have been negotiating for weeks on a draft resolution that would impose a fourth round of sanctions on Iran for refusing to halt its uranium enrichment program.

The proposal, drafted by the United States, calls for new curbs on Iranian banking, a full arms embargo, tougher steps against Iranian shipping, moves against members of Iran's Islamic Revolutionary Guard Corps and firms they control and a ban on new investments in Iran's energy sector.

Diplomats say that both Russia and China have problems with the proposed arms embargo, energy investment ban and other punitive measures included in the U.S. draft.

Washington and its allies had hoped the Security Council could vote on a new U.N. sanctions resolution by the end of last month, but diplomats say negotiations could drag on at least until June.