India has sharply escalated its response to the US Navy's strike on an oil tanker in the Gulf of Oman, with External Affairs Minister S. Jaishankar telling US Secretary of State Marco Rubio that the attack that killed three Indian sailors was "not justified" and demanding safeguards for civilian shipping operating in the conflict-hit region.

The unusually strong message from New Delhi came after Indian authorities confirmed that three crew members who had gone missing following the strike were found dead, turning what had initially been a rescue operation into a diplomatic flashpoint between two strategic partners.

In a post on X late Friday, Jaishankar said he had directly conveyed India's outrage to Rubio over the deaths of the Indian mariners.

"Spoke to US Secretary of State Marco Rubio this evening. I reiterated India’s strong protest at the attacks by the US Navy in the Gulf that killed three Indian mariners. Such lethal actions against commercial shipping are not justified," Jaishankar wrote.

Hours before Jaishankar's conversation with Rubio, the Ministry of External Affairs (MEA) summoned US Charge d'Affaires Jason Meeks and lodged a formal protest over what it described as the continuing attacks by American naval forces on commercial vessels carrying Indian crew members.

In a strongly worded statement, the ministry said the deaths were "tragic and avoidable" and warned that the use of deadly force against civilian shipping threatened the safety of international maritime trade.

"A strong protest was lodged regarding the continuing attacks by United States naval forces on commercial vessels carrying Indian sailors in the Gulf of Oman, which have already resulted in the tragic and avoidable loss of three Indian lives," the MEA said.

The ministry added that the use of lethal force against civilian shipping was unacceptable.

"Such actions are unacceptable and undermine the safety, security and stability of international maritime commerce in a sensitive region at a difficult time," it said.

India also urged Washington to ensure that US forces operating in the region take all necessary measures to prevent civilian casualties in future operations.

What happened in the Gulf of Oman?

The Palau-flagged oil tanker Settebello was carrying a crew of 28 when it came under attack in the Gulf of Oman.

Of them, 24 were Indian nationals, while the remaining four included two Pakistanis, one Ukrainian and one Russian.

Twenty-one Indian sailors were rescued after the incident. However, the three Indian crew members who had initially been reported missing were later confirmed dead by authorities.

Why did the US target the tanker?

The United States military has acknowledged carrying out the strike.

According to US Central Command (CENTCOM), the tanker was targeted after it allegedly failed to comply with repeated instructions from US naval personnel and was attempting to transport Iranian oil in violation of an ongoing American blockade linked to the wider regional conflict.

CENTCOM said one of its aircraft fired on the vessel and disabled it after the crew repeatedly ignored directions issued by US forces.

The American explanation, however, has not softened India's stance.

New Delhi has maintained that the vessel was engaged in commercial activity and carrying a large number of Indian nationals whose safety should have been protected.

The incident has unfolded against the backdrop of rising tensions in West Asia, where competing military actions and restrictions on maritime movement have disrupted global shipping routes.

India, one of the world's largest suppliers of seafarers to the international shipping industry, has repeatedly voiced concern over the impact of the regional conflict on civilian crews.

With IANS inputs