"This is a punitive resolution. I say this because I saw some comments yesterday from Moscow that it wasn't. It is," the US State Department's third highest diplomat Nicholas Burns told reporters after talks with Israeli officials in Jerusalem.
His comments came after Russia's foreign minister said the proposed text, being discussed on Thursday by ambassadors of the six major powers dealing with the Iran nuclear crisis, does not foresee fresh sanctions.
Envoys from the five veto-wielding permanent members of the Security Council - Britain, China, France, Russia and the United States - plus Germany are working to build on elements of a text agreed by foreign ministers in Berlin Tuesday, according to diplomats at the United Nations.
The new draft would slap a third set of economic and trade sanctions against Iran for defying Security Council demands to stop uranium enrichment activities that the West fears could be used to make a nuclear bomb.
"This resolution builds on the last two resolutions in many of the same categories," Burns said, mentioning a travel ban on certain Iranian officials, freezing of assets of some institutions and a ban on exports of dual-use items.
He said a resolution could be submitted on Thursday or Friday, but would probably need a few weeks of discussion before it can be brought to a vote in the 15-member Security Council.
"We are confident that it will pass, we know it is the right step. Iran is flagrantly out of compliance with its Security Council obligations," he said.
Russian Foreign Minister Sergei Lavrov had said on Tuesday that the draft resolution envisages direct talks with Tehran that would include the United States and that it does not foresee fresh sanctions.