The United States has served notice on India and 11 other major importers of Iranian oil that a decision on imposing financial sanctions on them would depend on progress in cutting down supplies from Tehran.

"I think that depends on the progress of those countries," State Department spokesman Victoria Nuland told reporters Wednesday when asked when was the US expected to take a decision on India, China and 10 other nations excluded from an exemptions list.

"You know where we are, that we'd like to see all of the countries that trade heavily in Iranian crude reduce their numbers," she said.

"So as we see the kind of progress that we saw with the EU and with Japan, then we'll look at doing more of these," Nuland said. "But conversations continue with those governments."

The United States Tuesday exempted Japan and ten European nations - Belgium, the Czech Republic, France, Germany, Greece, Italy, the Netherlands, Poland, Spain, and the United Kingdom - from US sanctions for having significantly reduced purchases of Iranian crude oil.

Asked if like Japan, 15 to 22 percent cut was the benchmark US expected from the 12 remaining countries, Nuland said: "The circumstances in Japan were particularly acute after the earthquake, tsunami, and the loss of their nuclear power plants."

"Even in those extreme conditions where one could argue their dependence might have gone up, they were able to cut by 15 to 20 percent," she noted adding, "So one would hope that countries can do as much as they possibly can."

"We all have the same goal here, which is for these sanctions to really pinch Iran and make it think twice about its nuclear weapons programme, and convince it to come clean," Nuland said.

"So the more countries can do, the more we have the impact that we desire."

Asked about US expectations from India, Nuland declined "to talk about our specific negotiations with individual countries."

"But we are continuing to have productive discussions with India, and they have some choices that they'll need to think about making."