The North Atlantic Treaty Organization (Nato) and European Commission have joined a growing chorus of criticism against Iran following an attack on a Zodiac Maritime tanker.

The incident, off Oman, claimed the lives of a UK national and a Romanian crew member.

The comments from Nato and the EC come shortly after the UK, the US, Romania and Israel all pointed the finger at Tehran for the use of military drones against Zodiac's 49,992-dwt tanker Mercer Street (built 2013).

“Freedom of navigation is vital for all Nato allies, and must be upheld in accordance with international law,” Nato said in a statement.

“The UK, the US, and Romania have concluded that Iran is highly likely responsible for this incident. Allies remain concerned by Iran's destabilising actions in the region, and call on Tehran to respect its international obligations.”

Tit for tat

The attack against the tanker Mercer Street came amid what appear to be a series of tit-for-tat attacks by Israel and Iran whose targets have included shipping in the Middle East. The drone attack on the Mercer Street is the first of the incidents to claim seafarers’ lives.

Zodiac is controlled by Israeli billionaire Eyal Ofer.

“The exact circumstances of this attack have to be clarified and we take note of investigations carried out by the US, the UK and Israel," EC spokeswoman Nabila Massrali told reporters at a press conference. “This is an action that was against freedom of navigation in this area, and of course unacceptable.”

The UK’s secretary of state for foreign, commonwealth and development affairs Dominic Raab welcomed the Nato statement.

“We believe this was a deliberate, targeted attack by Iran,” he said on Twitter. “It must end its destabilising actions immediately.”

But Iran has denied the allegations.

Iran has summoned the British Charge d'Affaires in Tehran and a Romanian envoy to protest against the accusations.

Iranian foreign ministry spokesman Saeed Khatibzadeh said the allegations "were contradictory, false and provocative". He said Iran would respond if any action is taken against it.