Diplomats from the five permanent Security Council members – the United States, Britain, France, Russia and China – and Germany are meeting nearly every day in New York to revise a US-drafted sanctions proposal that Moscow and Beijing would like to see watered down, Western diplomats say.
"If you look at where we were six months or so ago, it was very difficult to point to any common ground amongst all of the permanent members of the Security Council," William Burns, under secretary at the US state department told journalists in Cape Town.
"Now you've seen recent statements not only from Russia but from China as well ... we are making significant progress."
"I believe we will produce significant measures in a resolution," he said.
Iran, the world's fifth-largest oil exporter, says its nuclear program is entirely peaceful and not intended for military use.
But the uranium enrichment program is in defiance of three rounds of UN Security Council sanctions which have spurred moves for even harsher measures to halt what the West fears is a covert nuclear weapons drive.
Burns said the new sanctions text was a unique opportunity for the global community, which has not always spoken with one voice on nuclear disarmament and technology, to signal its unhappiness over Iran's nuclear program.
"In many ways (it is) a unique opportunity to send a unified international message about international concern, in this case about Iran's failure to live up to its obligations," he said, given the complicated process of give-and-take negotiations.