New Delhi: India has seized three oil tankers sanctioned by the United States and reportedly linked to Iran this month, while ramping up surveillance across its maritime zone to curb illicit trade, a source with direct knowledge of the matter told Reuters on Monday.

The three vessels, Stellar Ruby, Asphalt Star, and Al Jafzia, frequently changed identities to evade coastal law enforcement, the source said. Their owners are based overseas.

According to the source, India is aiming to ensure that its waters are not used for ship-to-ship transfers designed to mask the origin of oil cargoes. The National Iranian Oil Company, however, denied any connection of the three tankers with the firm.

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The seizures come amid strengthening ties between Washington and New Delhi.

In a related development, US military forces boarded another sanctioned tanker in the Indian Ocean after tracking it from the Caribbean, targeting illicit oil connected to Venezuela, the Pentagon said Sunday.

Venezuela, subject to US oil sanctions for several years, relied on a shadow fleet of falsely flagged tankers to move crude globally. President Donald Trump had imposed a quarantine on sanctioned tankers in December to pressure then-President Nicolás Maduro, who was apprehended in January during a US military operation.

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Several tankers fled the Venezuelan coast following the raid, including the vessel boarded in the Indian Ocean. The Defence Department said in a post on X that US forces boarded the Veronica III, conducting “a right-of-visit, maritime interdiction and boarding.”

“The vessel tried to defy President Trump’s quarantine — hoping to slip away,” the Pentagon said. “We tracked it from the Caribbean to the Indian Ocean, closed the distance, and shut it down.”