The MV Mercer Street, operated by the London-based company Zodiac Maritime, was off Oman’s coast in the Arabian Sea when the incident occurred on Thursday.
But Israeli Foreign Minister Yair Lapid on Friday blamed “Iranian terrorism”.
“Iran is not just an Israeli problem,” Mr Lapid said in a statement, adding: “The world must not be silent.”
However, details of the attack on the Liberian-flagged, Japanese-owned tanker remain unclear. Iran has not yet commented on the allegations.
A spokesperson for the UK government said it was also trying to “urgently establish the facts”.
“Our thoughts are with the loved ones of a British national who has died following an incident on a tanker off the coast of Oman,” the statement said.
It added that vessels “must be allowed to navigate freely in accordance with international law”.
The company added that the vessel was now “sailing under the control of her crew” and heading to a safe location with a US naval escort.
The undeclared “shadow war” between Israel and Iran appears to be hotting up.
But this attack marks a significant escalation with its human casualties.
Israeli Foreign Minister Yair Lapad called for a tough response and said he was in consultation with his British counterpart Dominic Raab, and that the issue would be taken to the UN.
An unnamed Israeli official said it would be hard for Israel to turn a blind eye to the attack.