Calling it a "unlawful and callous attack," British Foreign Secretary Dominic Raab said his country and its allies planned a coordinated response over the strike on Thursday on the oil tanker Mercer Street.

It marked the first-known fatal attack after years of assaults on commercial shipping in the region linked to tensions with Iran over its tattered nuclear deal.

While no one has claimed responsibility for the attack, Iran and its militia allies have used so-called "suicide" drones in attacks previously, which crash into targets and detonate their explosive payloads.

However, Israel, the UK and the responding US Navy have yet to show physical evidence from the strike or offer intelligence information on why they blame Tehran.

Israeli Prime Minister Naftali Bennett went further than Raab in remarks on Sunday, staring directly into the camera and slowly warning: "We know, at any rate, know how to convey the message to Iran in our own way."

The drone attack blasted a hole through the top of the oil tanker's bridge, where the captain and crew command the vessel, a US official said. The blast killed two crew members from the United Kingdom and Romania.

In his statement, Raab said it was "highly likely" Iran attacked the tanker with one or more drones.

"We believe this attack was deliberate, targeted and a clear violation of international law by Iran," he said. "Iran must end such attacks, and vessels must be allowed to navigate freely in accordance with international law."

Earlier, Iranian Foreign Ministry spokesman Saeed Khatibzadeh described the allegation Iran carried out the attack as "baseless."

From Jerusalem, Bennett offered condolences to both the United Kingdom and Romania for the killing of their citizens. He said Israeli intelligence had evidence linking Iran to the attack, but did not offer it.

Other Israel-linked ships have been targeted in recent months as well amid a shadow war between the two nations, with Israeli officials blaming the Islamic Republic for the assaults. Shipping in the region began being targeted in the summer of 2019, about a year after then-President Donald Trump unilaterally withdrew America from Iran's nuclear deal with world powers.

Israel meanwhile has been suspected of conducting a series of major attacks in Iran and on Iranian shipping. Also, Iran saw its largest warship recently sink under mysterious circumstances in the nearby Gulf of Oman.

The Mercer Street, owned by Japan's Taihei Kaiun Co, is managed by London-based Zodiac Maritime, part of Israeli billionaire Eyal Ofer's Zodiac Group. In early July, the Liberian-flagged container ship CSAV Tyndall, once tied to Zodiac Maritime, suffered an unexplained explosion on board while in the northern Indian Ocean, according to the US Maritime Administration.

The attack marks the first major confrontation with Iran for Bennett, who took over as premier in June after a coalition deal unseated Israel's long-serving Prime Minister Benjamin Netanyahu.

Netanyahu is suspected of launching a series of attacks targeting Iran, including explosions at the country's main enrichment site and the killing of a prominent military nuclear scientist.

Australian Associated Press