An Israel-affiliated merchant vessel was struck by an uncrewed aerial vehicle off India's west coast, British maritime security firm Ambrey said on Saturday, in the first such known attack so far away from the Red Sea since the Gaza war.

A fire on the Liberian-flagged tanker was extinguished without crew casualties in the incident 200 km (120 miles) southwest of the Indian city of Veraval, it said, adding some "structural damage was also reported and some water was taken onboard".

"Merchant vessels are advised these types of attacks are typically targeted at Israel-affiliated shipping, but have in the past mistakenly hit previously Israel-affiliated vessels," Ambrey said. "This event fell within Ambrey's Iranian UAV heightened threat area."

An Indian Navy official told Reuters that it responded to a request for assistance last morning.

"The safety of crew and ship has been ascertained. The Navy has also dispatched a warship to arrive in the area and provide assistance as required," the official said, declining to be named as he was not authorised to discuss the incident.

Indian news agency ANI, in which Reuters has a minority stake, identified the tanker as MV Chem Pluto carrying crude oil from Saudi Arabia. Citing Indian defence sources, ANI said the tanker had around 20 Indians on board.

A Reuters tracker showed the ship was headed towards the Port of Mangalore in India's south.

The hit on the vessel follows drone and missile attacks in the Red Sea by Iran-backed Houthis, who say they are supporting Palestinians under siege by Israel in the Gaza Strip, on commercial shipping, forcing shippers to change course and take longer routes around the southern tip of Africa.

US on Friday said Iran was "deeply involved" in planning operations against commercial vessels in the Red Sea and its intelligence was critical to enable Yemen's Houthi movement to target ships.

"We know that Iran was deeply involved in planning the operations against commercial vessels in the Red Sea. This is consistent with Iran's long-term materiel support and encouragement of the Houthis' destabilizing actions in the region," White House national security spokeswoman Adrienne Watson said in a statement.

"This is an international challenge that demands collective action," Watson said.

Iran denies involvement in attacks by the Houthis in the Red Sea.