Nayara shipped in about 175,000 barrels per day (bpd) of oil from Iran in April, an increase of 32 percent from March, the data showed, Reuters wrote.
The sources declined to be identified as they were not authorized to speak with the media.
Iran is India's third biggest energy supplier, selling it around 18.4 million tons of crude oil during 10 months between April 2017 and January 2018, according to provisional data from India's petroleum ministry.
Indian crude oil importers say they will adhere to their term supply contract obligations with the Persian Gulf producer, undeterred by Washington's efforts to restrain Iran's oil sales.
India's flagship state-run refiner Indian Oil Corporation (IOC) holds a term contract with Iran to receive 180,000 barrels per day (bpd) in the current fiscal year ending March 2019.
India was among a select group of countries which maintained oil purchases from Iran when the country came under intensified Western sanctions in 2011.