India has made "tremendous progress" in reducing oil imports from Iran, a senior U.S. government official said on Friday, in a sign the South Asian nation is likely to get a third waiver from sanctions imposed by Washington against Tehran's nuclear programme.

"All of the data is certainly pointing in a positive direction," U.S. Under Secretary for Political Affairs Wendy Sherman told reporters when asked about a possible waiver to India.

U.S. and European Union sanctions are aimed at choking the flow of oil money into Iran and forcing Tehran to curb its controversial nuclear programme. As a result, Iran's crude exports were halved in 2012, costing it as much as $5 billion a month.

All of Iran's major Asian clients - China, India, Japan and South Korea - have cut import volumes to secure waivers that allow them to continue the shipments without the risk of losing access to the U.S. financial system.