G7 foreign ministers on Friday said "all available evidence clearly points to Iran" being behind a drone strike on July 29 against an Israel-linked tanker that killed a former British soldier and Romanian national.

"This was a deliberate and targeted attack, and a clear violation of international law... There is no justification for this attack," the ministers from the world's seven most developed nations said in a statement.

Iran has strongly denied having any link to the attack on the MV Mercer Street, which came as tensions grow in the region and talks to revive the 2015 deal on the Iranian nuclear programme at a standstill.

But European countries and the United States renewed their accusations at a closed-door Security Council meeting at UN headquarters in New York Friday.

"The UK knows that Iran was responsible for this attack. We know it was deliberate and targeted," said British Ambassador to the UN Barbara Woodward, who added the evidence was "clear cut".

"The door for diplomacy and dialogue remains open. But if Iran chooses not to take that route, then we would seek to hold Iran to account and apply a cost to that," she told reporters.

The MT Mercer Street tanker is seen off the UAE emirate of Fujairah on August 3, 2021
The MT Mercer Street tanker is seen off the UAE emirate of Fujairah on August 3, 2021 AFP / Karim SAHIB

The UN Security Council is due to discuss the incident further at an open meeting on maritime security on Monday.

The G7 ministers said "vessels must be allowed to navigate freely in accordance with international law" and vowed to "do our utmost to protect all shipping, upon which the global economy depends".

"Iran's behaviour, alongside its support to proxy forces and non-state armed actors, threatens international peace and security," they said, calling on Tehran to stop all activities inconsistent with UN Security Council resolutions.

The United States and Israel have both pointed the finger at Iran for being behind the attack on the tanker, which is managed by a prominent Israeli businessman in London.

Security analysts have said the fatal attack upped the stakes in the "shadow war" against vessels linked to Iran and Israel.

On Tuesday, Iran was again blamed for an alleged hijacking of an asphalt and bitumen tanker in the Gulf of Oman, prompting more denials from the Islamic republic.

The tensions have come as hardline former judiciary chief Ebrahim Raisi took over this week as Iranian president following his victory in June elections, replacing Hassan Rouhani who was seen as a more moderate figure.