Three tankers including a Qatari LNG vessel were struck within hours in the Strait of Hormuz, maritime monitors and Qatar said on Tuesday, with peace mediator Doha denouncing an “unacceptable” Iranian attack.

An “unknown projectile” hit a tanker overnight, causing a fire, before two more were hit, at least one by a drone, British maritime security agency UKMTO said.

The string of attacks after more than a week of respite revived concerns about freedom of navigation after Iran lifted its blockade of the vital waterway following a fragile ceasefire with the United States.

All three vessels were struck close to Oman. Oman had proposed a temporary transit corridor hugging its coastline in an initiative opposed by Iran, which wants to charge ships using the narrow waterway.

Qatar, which helped broker the truce, blamed Iran for the attack on its tanker and urged Tehran to “cease all practices that undermine regional security or threaten the safety of international maritime navigation”.

“The targeting of the Qatari vessel ‘Al-Rekayyat’ while transiting near the Strait of Hormuz constitutes an unacceptable attack on the security and safety of international maritime navigation,” Doha’s foreign ministry spokesman Majed Al Ansari wrote on X.

“We hold Iran fully legally responsible for this attack and for any resulting damages or repercussions,” he added.

The attacks came despite the ceasefire between the US and Iran in the Middle East war, which began with US-Israeli strikes on Tehran in late February.

The future of Hormuz, the main route for Gulf energy exports, has been a sticking point during talks between Tehran and Washington to permanently end the conflict.

‘Clear signal’

“We are now in a sensitive period where potential alternatives to an Iranian toll or fee system are being explored,” Andreas Krieg, a security expert at King’s College London, told AFP.

“Iran is sending a clear signal that no alternative will be accepted.

“Tankers trying to diverge through the Omani maritime corridor without registering with the Iranian authority will be punished,” Krieg added, calling it a “clear violation” of the ceasefire agreement and international law.

US news outlet Axios reported late on Monday that Iran had “fired at least two missiles at commercial ships”, citing two unnamed US officials.

The Pentagon did not immediately respond to an AFP request for comment.

Maritime traffic had tentatively resumed after Washington and Tehran signed a memorandum of understanding last month aimed at ending the conflict and reopening the strategic route.

However, Iran has insisted there will be no return to pre-war arrangements, under which vessels could pass freely through the strait.

Under the 14-point US-Iran memorandum of understanding, Iran and Oman, which border Hormuz, must hold talks “to define the future administration and maritime services” in the key waterway with other Gulf states.

Qatar had previously refused to enter into mediation under Iranian fire as Tehran launched an unprecedented aerial bombardment against Gulf states in retaliation for the US-Israeli strikes.

However, Doha has played an increasingly active role in negotiations, hosting indirect talks between Iran and the US last week.