UNITED NATIONS - Top diplomats from the world's major powers will try to reach agreement Saturday on new sanctions against Iran for refusing to suspend uranium enrichment. A US official predicted the session would lead to a "substantive resolution."

A general view shows the Bushehr nuclear power plant in the Iranian Persian Gulf port of Bushehr, 1,200 Kms south of Tehran, in June 2006. [AFP]

Foreign ministry political directors from the United States, Russia, China, Britain, France and Germany held a two-hour conference call Thursday to discuss what to include in the resolution - and they were scheduled to hold another conference call Saturday morning.

The six countries indicate they want to move quickly to strengthen sanctions following last week's report by the International Atomic Energy Agency that Iran was expanding enrichment instead of suspending it.

Iran's refusal to freeze all its enrichment-related activities prompted the Security Council on Dec. 23 to impose sanctions targeting its nuclear and missile programs. The council gave Tehran 60 days to halt enrichment or face additional nonmilitary measures.

"This will be a substantive resolution. This will be something that will ... increase diplomatic pressure on Iran, on the Iranian regime," US State Department deputy spokesman Tom Casey said Friday.

"They have gotten agreement on the major elements," he said. "We do expect that the remaining issues in terms of the main components of the resolution will be resolved on Saturday and that the drafting can begin."

If agreement is reached, the UN Security Council will start drafting a new resolution next week.

South Africa's UN Ambassador Dumisani Kumalo, the current council president, said he understands that the 10 non-permanent council members would have input in the new resolution - unlike the Dec. 23 measure which was drafted by the six nations and presented to the rest of the council to vote on.

A British Foreign Office spokesman, speaking on condition of anonymity in line with government policy, refused Friday to discuss details of Thursday's conversation but acknowledged there were still differences between nations.

Britain's UN Ambassador Emyr Jones Parry said recently that the new resolution would be looking at an "incremental" strengthening of sanctions - and the word "incremental" has been repeated by other council diplomats.

Some diplomats said the new measure may include travel bans, expand the list of technology and materials countries are banned from making available to Iran, and create stiffer economic sanctions including a ban on export guarantees to Iran, among other options.

The diplomats spoke on condition of anonymity because the negotiations are private.

The French Foreign Ministry, in a statement Friday, said the phone conversation of political directors showed that the six countries were "fully in agreement on the framework of the next step" at the Security Council.

The ministry said the current sanctions could be strengthened "for example, by designating new people or new entities hit by restrictive measures ... and through complementary measures." It didn't elaborate on what those measures might be.

UN diplomats said the six countries all believe the initial sanctions have had a positive effect on Tehran.

Iran insists its nuclear program is aimed solely at producing nuclear energy - not nuclear weapons - and it has adamantly refused to halt it.

German Foreign Ministry spokesman Martin Jaeger called the talks "constructive and productive" and said they are being conducted "with great intensity."

Russia's Deputy Foreign Minister Sergei Kislyak was quoted by the Interfax news agency as saying "the main thing is that all sides are united in their wish to find a political resolution of the problems."