The envoys of the Security Council's five permanent members -- Britain, China, France, Russia and the United States -- plus Germany held a 45-minute session at Britain's UN mission in New York but did not produce a text.

"Some good progress. It was a good exchange of views," Russian Ambassador Vitaly Churkin said, but ruled out agreement on a draft this week.

On instructions from their governments, the six ambassadors on Monday began discussing elements of a new draft sanctions resolution.

The new measures, which would tighten sanctions adopted by the council in December in the face of Tehran's nuclear defiance, include a travel ban on officials involved in illicit nuclear work, barring Iran from exporting arms, financial sanctions and possible restrictions on export credits to Iran, diplomats said.

"We are just taking stock on where we are. There's been a lot conversation between capitals. So we are comparing notes, make sure everyone is on the same page," US acting ambassador Alejandro Wolff.

Li Junhua, the number three at China's UN mission, said the six envoys would meet against Friday morning to try to make further progress.

Earlier Thursday US Under Secretary of State Nicholas Burns held a conference call with his counterparts from Britain, China, France, Russia and Germany and then spoke separately with each of the five over the sanctions proposals, State Department spokesman Sean McCormack said.

"We're chipping away at any remaining differences that might exist," McCormack said.

But the talks have since bogged down, with a senior US official saying one problem was Chinese objections to elements in the sanctions proposal.

"We're working through some stuff with them," the official, speaking on condition of anonymity, said of the Chinese.

The December sanctions were adopted by the 15-member Security Council after Tehran refused to freeze a uranium enrichment program that could produce fuel for nuclear power stations but also material to make atomic bombs.

That resolution set a 60-day deadline for Iran to suspend its program. When the deadline passed in late February, the UN atomic watchdog reported that Iran had actually accelerated its enrichment activities.

P5+1 diplomats have described the second sanctions proposal as an "incremental" ratcheting up of the December measures, which included a ban on the sale of nuclear and ballistic missile-related materials to Iran and a freeze on assets of individuals or companies involved in the programs.

Negotiations on the December resolution dragged on for months, mainly due to efforts by Russia, which has extensive energy and other dealings with Iran, to water down the measures.

McCormack insisted Russia was not the problem in the current round of talks.

The US spokesman expressed optimism that despite ongoing differences the new sanctions resolution would be passed quickly, though he declined to set any timeframe.

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