Diplomats said envoys of the six nations concluded after another bargaining round Tuesday that they still needed clarification and instructions from their capitals before signing on to a compromise draft resolution that could be submitted to the Council's 10 non-permanent members.

The meeting brought together ambassadors of the council's five permanent members -- Britain, China, France, Russia and the United States -- plus Germany, a day after British Ambassador Emyr Jones Parry reported "substantial progress" in agreeing to tighten the sanctions adopted by the council in December.

French Ambassador Jean-Marc de La Sabliere said after Tuesday's session that the six would meet again Wednesday afternoon to resume bargaining and brief the rest of the council.

"I hope we will be able to give an agreed text to present to the (other) members of the council," he said.

His Russian counterpart Vitaly Churkin said the non-permanent members were briefed "in general terms" Tuesday but noted that several among the six ambassadors still "have issues that need to be resolved".

Among those issues, Chinese Ambassador Wang Guangya cited a proposal to extend an assets freeze to several officials and entities thought to be linked to Iran's nuclear and ballistic missile programs.

"For many, including China, we are not sure about all those entities, because the objective is to target the nuclear and missile activities. But now with so many names, we don't know if they are linked to those activities or not," Wang said. "That's why we need more information."

"We had a good discussion," US acting ambassador Alejandro Wolff said. "We are not at the point where we could say we are agreed on the overall approach."

The proposal would add an arms embargo as well as some financial and trade restrictions to the sanctions imposed on Iran in December after it spurned UN demands to halt sensitive nuclear fuel enrichment.

It would notably add several senior officers of Iran's elite Revolutionary Guards Corps to the list of officials subjected to an assets freeze.

The six powers have offered to suspend their sanctions against Iran if Tehran complies with UN demands, particularly by suspending uranium enrichment.

But an Iranian government spokesman reiterated earlier Tuesday that Tehran had no intention of suspending uranium enrichment, the key demand of the Security Council.

"The adoption of another resolution is unwelcome but is not worrying," Iranian government spokesman Gholam Hossein Elham told reporters. "It will not affect our work and will not concern our people."

However at a disarmament conference in Geneva, Iranian Foreign Minister Manouchehr Mottaki reiterated that Tehran was ready to offer "necessary" guarantees on its nuclear program if the issue was withdrawn from the Security Council.

He did not specify what guarantees Iran was prepared to give.

Tehran announced earlier this week that Mahmoud Ahmadinejad was intending to attend any crunch meeting of the Security Council in person to defend Iran's position but Elham insisted nothing had been confirmed.

The six powers want Iran to suspend uranium enrichment as they fear the process could be diverted away from civilian use to make nuclear weapons. Iran insists its nuclear program is entirely peaceful.