The letter was sent on Monday to traders who submit cargo offers into IOC’s regular crude oil buy tenders.
IOC bought 2 million barrels of Russian Urals for the first time in two years earlier this month.
A source at another state refiner, Bharat Petroleum Corp, said his firm mostly buys Urals on delivered basis, whereby freight and insurance are included, unlike in FOB. The source added that traders were not offering Russian barrels.
Russia and Kazakhstan are small suppliers to India. In December, the two countries accounted for 64,000 barrels per day (bpd) out of 4.7 million bpd.