New Delhi: India has escalated its protest over the killing of three Indian mariners by the US military off the coast of Oman, with External Affairs Minister S Jaishankar calling his counterpart Marco Rubio and making the point that killing of civilians cannot be justified.The minister called Rubio after US forces carried out at least three strikes on merchant vessels off the coast of Oman that had Indian crewmembers on board as part of its efforts to blockade Iran. While several Indians were rescued in coordination with Oman, three were killed when a Hellfire missile was fired on a tanker this week."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 posted on Saturday.Sources said that the US side has agreed to look into the matter and examine the circumstances that led to the killing of civilians.The killings of three Indians has evoked a strong reaction domestically and the incident will cast a shadow over the possible meeting between Prime Minister Narendra Modi and US PresidentTrump at the sidelines of the G7 summit in Paris next week.India has twice summoned the US charge d'affaires Jason Meeks to lodge a strong protest after ongoing strikes by the US military, even as President Donald Trump accused Iran of trying to hit Indian ships.While the US Central Command has taken responsibility for the attacks and even posted videos of the strikes Trump seemed to accuse Iran of attempted attacks. "Their (Iran's) totally rebuffed Drone attack last night against Indian Ships leaving the Hormuz Strait is totally unacceptable," he posted on Friday.Meeks was summoned on Friday as well as Wednesday and conveyed strong protest by India over the continued US military action. Palau-flagged oil tanker Marivex with 24 Indian seafarers was disabled by US forces on June 8, with no injuries reported. On June 10, Palau-flagged tanker, Settebello, was struck, killing three of the 24 Indian sailors. On Thursday, MT Jalveer, a Guinea-Bissau-flagged tanker with 20 Indians, was attacked.