India has seized three U.S.-sanctioned oil tankers linked to Iran this month and increased surveillance in its maritime zone to combat illicit trade, a source confirmed on Monday.

This follows a post on X by Indian authorities earlier in February, which was later deleted, The Caspian Post reports, citing Reuters.

India aims to prevent its waters from being used for ship-to-ship transfers that obscure the origin of oil cargoes, the source with direct knowledge of the matter told Reuters.

The seizures and heightened surveillance follow an improvement in U.S.-India relations. Washington earlier this month announced it will cut import tariffs on Indian goods to 18% from 50%, after New Delhi agreed to stop Russian oil imports.

The three sanctioned vessels - Stellar Ruby, Asphalt Star and Al Jafzia - frequently changed their identities to evade law enforcement by coastal states, the source said, adding that their owners were based overseas.