The official, who spoke on condition of anonymity to preview Clinton's private discussions in Kolkata and New Delhi, said the "trend lines are good" but "we really need to receive assurances that they are going to continue to make good progress."
Like other major consumers of Iranian oil, India could face US sanctions by the end of June if the Obama administration determines it has not made significant cuts in imports under a law aimed at squeezing Iran's petroleum industry to press the country to comply with international demands over its nuclear program.
A dozen European nations and Japan have already been spared from those sanctions after the administration determined they had substantially reduced their Iranian oil imports. India, along with China, South Korea, Turkey and South Africa, has still not received such waivers.
India imports around 70 percent of its oil, and about 9 percent of the imports are from Iran. The US official said India had recently stepped up imports of oil from Saudi Arabia to make up for the reduction in Iranian oil and that the US was eager to see the Indians explore other alternatives. Iran is India's second-largest crude oil supplier after Saudi Arabia and according to media reports imports 550,000 barrels a day.