"I'm not familiar with the evidence that you are citing," Hook said, adding India was not violating the US sanctions.
US President Donald Trump last year withdrew from the 2015 nuclear deal between Iran and world powers and revived a range of sanctions against the Persian Gulf nation.
It, however, granted a six-month waiver from sanctions to eight countries - China, India, Japan, South Korea, Taiwan, Turkey, Italy and Greece, but with a condition that they would reduce their purchases of Iranian oil.
The Trump administration in April decided not to renew waiver that let countries like India buy Iranian oil without facing US sanctions.
India, which is the second biggest purchaser of Iranian oil after China, had agreed to restrict its monthly purchase to 1.25 million tonne or 15 million tonne in a year (300,000 barrels per day), down from 22.6 million tonne (452,000 barrels per day) bought in 2017-18 financial year.