The U.S. Navy, which was escorting the tanker with the USS Ronald Reagan aircraft carrier, said on Saturday that early indications "clearly pointed" to a drone attack.
The United States formally blamed Iran for carrying out an attack on an Israeli-managed petroleum tanker off the coast of Oman, warning of an "appropriate response."
The deadly drone strike Thursday killed a British national and a Romanian. The U.S. and Britain pledged to work with allies to respond, while Iran on Sunday denied it was involved in the attack, after it was blamed by Israel.
"Such blame games are nothing new," Iranian Foreign Ministry spokesman Saeed Khatibzadeh said in quotes by Reuters.
Dominic Raab, British Foreign Secretary, said Britain's assessments had concluded it was highly likely that Iran had used one or more drones to launch the strikes, Reuters reported.
The merchant tanker, "Mercer Street," was hit twice. The first attack did not cause any major damages but the second strike hit the rooms of the crew, according to Axios.
Mercer was owned by a Japanese company but was managed by Israeli-owned Zodiac Maritime. According to Israeli authorities, this was the reason the ship was targeted, the report said.
The drone strikes marked the first-known deadly assault after years of attacks on commercial shipping in the region tied to frictions with the Islamic republic over its fractured nuclear agreement.
Bennett said that they are certain the drone attack was intentional and "a clear breach of international law" by Iran.
He said Britain was working with international partners to carry out a "concerted response."
UK and Israeli officials said their next plan of action will be to try to convene a meeting of the United Nations Security Council, Axios said.
The U.S. Navy, which was by the side of the ship as escort aloong with the USS Ronald Reagan aircraft carrier, said early signes pointed to a drone strike.
Frictions have deepened in the Gulf region since Washington re-enforced economic sanctions on Iran in 2018 after former President Donald Trump backed out of Tehran's 2015 nuclear agreement with allies.