Gulf of Oman tanker attacks: What we know

The Norwegian-owned tanker Front Altair, carrying 75,000 tonnes of naphtha, was set ablaze

On 13 June, two tankers were damaged by explosions in the Gulf of Oman, a strategic waterway crucial to global energy supplies.

It was the second time in a month tankers have been attacked in the region and came amid escalating tension between Iran and the United States.

US Secretary of State Mike Pompeo swiftly accused Iran of being behind the attacks. He said the assessment was based on the "intelligence, the weapons used, the level of expertise needed to execute the operation, recent similar Iranian attacks on shipping, and the fact that no proxy group operating in the area has the resources and proficiency to act with such a high degree of sophistication".

But a senior Iranian official insisted Iran had "no connection with the incident".

What happened on 13 June?

The Marshall Islands-flagged Front Altair and Panama-flagged Kokuka Courageous were both sailing south-eastwards through international waters, after passing through the Strait of Hormuz, when they were rocked by explosions.

The US Navy received a call from the Front Altair saying it had been attacked at 03:12 GMT, when it was 19 nautical miles (35km) south of Iran's coast, while the Kokuka Courageous reported being hit at 04:00, 21 nautical miles off Iran.

FRONT ALTAIR

The tanker was carrying 75,000 tonnes of naphtha from the United Arab Emirates to Taiwan.

Its owner, Norwegian company Frontline, said an explosion had occurred on the vessel, triggering a fire. The 23 crew members on board were not harmed and were rescued by the cargo ship Hyundai Dubai, it added. They were subsequently carried by an Iranian naval vessel to the port of Jask.

Frontline said the fire on board the tanker was extinguished by emergency responders within hours of the incident, and that no marine pollution was reported.

Photographs and video published by Iranian media showed a fire on Front Altair's starboard side, and a huge column of black smoke towering above it.

Satellite imaging company Iceye said that its data suggested there was "a non-trivial amount of oil around the vessel on the surface of the sea" on 14 June.

With colours altered to enhance contrast, apparent oil slicks can be seen upon the surface

Frontline said the cause of the explosion remained unknown, but that it had "ruled out the possibility that it was caused by mechanical or human error".

Taiwan's state oil refiner CPC Corp, which had chartered the Front Altair, initially said the vessel was "suspected of being hit by a torpedo". The master of the Hyundai Dubai also reported in a distress call that the Front Altair's master believed the explosion was the result of a "torpedo attack".

No close-up images of the damage to the vessel's hull have been released, but the crew of a tug that helped put out the fire was heard saying on the radio that there was a large hole just above the waterline.

Firefighters managed to extinguish the blaze on board the Front Altair

The US military said a US aircraft observed an Iranian Islamic Revolution Guard Corps (IRGC) Hendijan class patrol boat and several IRGC fast attack craft in the vicinity of the Front Altair at 05:09 GMT.

The US military also reported that the Iranian authorities had asked the Hyundai Dubai to "turn over the crew" to the IRGC fast attack craft, and that the Hyundai Dubai had complied with the request.

The Front Altair was being towed to the UAE port of Khor Fakkan on 16 June. Once there, the damage will be assessed and a decision will be made concerning the transfer of the naphtha.

KOKUKA COURAGEOUS

The tanker's managers, Bernhard Schulte Shipmanagement, said it had sustained damage to its hull on the starboard side following a "security incident". There was also an engine room fire, which was extinguished with CO2.

A hole could be seen in the hull of the Kokuka Courageous above the waterline

The 21 crew members were evacuated the vessel as a precaution and were picked up by the Dutch tug Coastal Ace. They were later transferred to the USS Bainbridge, a guided-missile destroyer, which was nearby after responding to the Kokuka Courageous distress call. One crewman was slightly injured in the incident and received first aid on board the Bainbridge.

The crew later returned to the Kokuka Courageous and restored emergency power.

The tanker arrived safely at the UAE port of Kalba on 16 June. A damage assessment and preparation for the transfer of the ship's cargo would commence once the port authorities had completed standard security checks, Bernhard Schulte Shipmanagement said.

The USS Bainbridge, a guided-missile destroyer, picked up the crew

The company did not speculate on the cause of the damage to the Kokuka Courageous. But the president of the vessel's owner, Japanese firm Kokuka Sangyo, reported that it was hit by two explosions in the space of three hours before the crew were evacuated.

Yutaka Katada told reporters on 14 June that he believed the tanker was hit by a "flying object".

"The crew told us something came flying at the ship, and they found a hole," he said. "Then some crew witnessed the second shot."

Mr Katada spoke after the US military had released grainy black-and-white video footage it said showed the crew of an IRGC Gashti Class patrol boat removing an "unexploded limpet mine" attached to the starboard side of the Kokuka Courageous, above the waterline amidships, at 1310 GMT on 13 June. The crew of the Kokuka Courageous had abandoned ship after discovering the mine, it added.

On 17 June, the US military released several colour photographs taken by its personnel to back up its allegations.

The US military said it filmed the crew of a Revolutionary Guard boat removing an unexploded limpet mine from the hull of the Kokuka Courageous

This photo shows the remnants of the unexploded mine, according to the US military

One of the new images showed what it said was the "the aluminium and green composite material left behind following [the] removal of an unexploded limpet mine" by the IRGC patrol boat's crew.

Also visible were holes purportedly created by nails used to hold the mine in place.

Other images showed the damage to the Kokuka Courageous' hull, 1m above the waterline at the aft, which the military said measured 1.1m by 1.5m (3.6ft x 4.9ft) and was "consistent with a limpet mine attack".

The US military said this hull damage was "consistent with a limpet mine attack"

What happened in May?

Four tankers were damaged by explosions within the UAE's territorial waters in the Gulf of Oman, east of the emirate of Fujairah, in the early hours of 12 May.

The vessels were the Saudi Arabia-flagged Amjad and Al Marzoqah, the Norwegian-flagged Andrea Victory, and the UAE-flagged tanker A Michel.

The four vessels damaged off the UAE coast in May did not have to be evacuated

There were no casualties, but the explosions blew holes in the tankers' hulls. Saudi Arabia's government said the two Saudi ships had suffered "significant" damage.

A report presented by the UAE to UN Security Council members said the blasts were the result of "a sophisticated and co-ordinated operation carried out by an actor with significant operational capacity, most likely a state actor".

The report said the operation involved small, fast boats and trained divers, who were likely to have placed limpet mines with a high degree of precision on the vessels' hulls below the waterline. Their intention, investigators concluded, was to disable the vessels but not destroy them. The four explosive charges were all detonated within less than an hour, according to the report.

Photographs released by the UAE authorities showed damage to the hulls of (clockwise from top left) the Amjad, Al Marzoqah, Andrea Victory and A Michel

The report stopped short of directly accusing a particular country.

However, Saudi Arabia's permanent representative to the UN, Abdallah al-Mouallimi, said it believed that "responsibility for this action lies on the shoulders of Iran", saying: "We believe there is enough evidence to demonstrate that."

US National Security Adviser John Bolton has said the explosive charges were "naval mines almost certainly from Iran", without providing any evidence. A US destroyer in the region also reportedly tracked 20 Iranian military boats entering UAE waters a few hours before the explosions.

Iran dismissed Mr Bolton's accusation that it was involved as "ridiculous".