TEL AVIV: Israel's key allies, the United States and Britain, joined it on Sunday in blaming Iran for a deadly tanker attack off Oman despite Tehran's denials, and Washington vowed an "appropriate response."

The joining of the two superpowers might result in war between Israel and Iran, observers said.

The US and British statements came after Israeli Prime Minister Naftali Bennett said there was "evidence" linking Iran to the attack after the Islamic republic rejected its arch-foe's "baseless accusations."

The MT Mercer Street, managed by prominent Israeli billionaire Eyal Ofer, was attacked on Thursday off Oman. A British security guard and a Romanian crew member were killed in what the United States, Britain and the vessel's operator, Zodiac Maritime, said appeared to be a drone strike.

Israel had blamed Iran with Foreign Minister Yair Lapid saying Friday he had ordered its diplomats to push for UN action against "Iranian terrorism." On Sunday, Iran denied involvement and Foreign Ministry spokesman Saeed Khatibzadeh said Israel "must stop such baseless accusations."

"Iran will not hesitate for a moment to defend its... interests and national security," he told journalists. Shortly afterwards, Bennett accused Iran of "trying to evade responsibility for the event" in a "cowardly manner."

"I determine, with absolute certainty, that Iran carried out the attack against the ship," Bennett said. "The intelligence evidence for this exists and we expect the international community will make it clear to the Iranian regime that they have made a serious mistake," he said.

"In any case, we know how to send a message to Iran in our own way."

British Foreign Secretary Dominic Raab said London believed the attack was "deliberate, targeted and a clear violation of international law by Iran," and "UK assessments" showed Iran used "one or more UAVs" (unmanned aerial vehicles) to target the tanker.

"Iran must end such attacks and vessels must be allowed to navigate freely in accordance with international law," Raab said in a statement.

US Secretary of State Antony Blinken said Washington was "confident that Iran conducted this attack," and vowed that an "appropriate response" was forthcoming.

Later on Sunday, Lapid noted he had spoken with Blinken and Raab in recent days and that he was "pleased" that both countries "condemned these terrorist acts."

"Israel will continue to hold conversations with our allies around the world and work together to formulate the necessary steps to combat ongoing Iranian terror," Lapid said in a statement.

Israel's chief of staff has spoken to his British counterpart about "recent events in the region and common challenges faced by both countries," a statement said.

Retired general Yossi Kuperwasser told military radio Israel would probably follow two tacks - create global pressure against Iran and retain its ability to act "beyond the diplomatic realm."

Maritime analysts Dryad Global said Thursday's attack was the fifth against a ship connected to Israel since February.