In a statement, New Delhi condemned the attack on the vessel, the Settebello, saying of "the 24 Indian crew onboard, 21 Indians have been rescued thus far and three Indians are reportedly missing".

"Attacks on shipping in the region are deeply worrisome and a direct result of the ongoing conflict in the region. We reiterate our call for immediate de-escalation," the foreign ministry added.

A critical waterway for global fuel supplies, the Strait of Hormuz in the Gulf has been almost completely blocked since the start of the Middle East war, which began with US-Israeli strikes on Iran in late February.

Talks during a fragile ceasefire in place since April have failed to deliver a deal to reopen the strait.

Earlier, the United Kingdom Maritime Trade Operations agency reported an incident 20 nautical miles northeast of Sohar in Oman, saying the vessel had reported one casualty and two crew members missing.

"Local authorities have reported a tanker has experienced a fire in their engine room and are on the scene assisting with the evacuation of the crew," it said.

British maritime security company Vanguard Tech said the Palau-flagged tanker Settebello had "transmitted a distress call stating that its engine room had been struck by a missile while operating off Sohar in the Gulf of Oman" and that there was a fire on board.