Six ships have been attacked in the Gulf in less than 48 hours, bringing the total of vessels attacked since the start of the war to 18, according to reports by UK Maritime Trade Operations (UKMTO) and the maritime intelligence company Vanguard.
It comes as Iran's new supreme leader Mojtaba Khamenei vowed to keep blocking the Strait of Hormuz in his first public statement on Thursday.
Verified footage showed two tankers on fire in Iraqi waters at the north of the Gulf late on Wednesday and UKMTO reported the ships had been "struck by an unknown projectile".
Safesea Vishnu, a US-owned vessel heading to India, was hit by an "unmanned speed boat carrying explosives" which "rammed into it, resulting in a major fire onboard", Indian authorities said.
Video filmed from a small boat - and authenticated by BBC Verify - shows a large explosion on the Safesea Vishnu before the boat speeds away and those on board can be heard celebrating.
