What happened in the Gulf of Oman on Thursday?

Two oil tankers were attacked, leaving one ablaze and the other adrift, in the second such incident in a month near the strait of Hormuz, a major strategic waterway for world oil supplies.

Taiwan’s state oil refiner CPC said the Front Altair, owned by Norway’s Frontline, was hit at about 4am GMT while carrying a Taiwan-bound cargo of 75,000 tonnes of naphtha, a petrochemical feedstock. CPC said it was suspected the boat had been torpedoed but other reports suggested a mine attack was more likely. The crew were picked up by a passing boat and handed over to an Iranian rescue vessel.

The Kokuka Courageous sustained damage to its hull while transporting methanol from Saudi Arabia to Singapore, its owner, Bernhard Schulte Shipmanagement, said. The operator of the tanker suggested it was struck by a missile. A shipping broker told Reuters the blast might have been caused by a magnetic mine. Its crew was also rescued – one suffered burns on his hands and was treated by a US Navy medical team.

Play Video 0:32 Oil tanker filmed ablaze in the Gulf of Oman – video

Who is to blame?

The US military has released video footage it says shows an Iranian military patrol boat approach one of the two tankers. The blurry black and white footage, taken from the air, shows a small military boat alongside a tanker and someone standing up on the prow of the boat to remove an object from the tanker’s hull. The boat then pulls away from the tanker. It was unclear whether it was being alleged the Iranian sailors were detaching the mine in order to remove evidence.

Play Video 0:36 Footage US military claims shows Iranian patrol boat removing limpet mine from tanker – video

The US military also released a photo it claimed showed a mine on the side of the tanker and some damage to the hull.

Facebook Twitter Pinterest A picture released by US Central Command shows what the US military says is damage from an explosion (left) and a likely limpet mine on the hull of Kokuka Courageous. Photograph: Reuters

Iran has denied all responsibility and its foreign minister suggested others could be trying to provoke a conflict between Iran and the US.

What happened in the incident in May?

On 12 May, four oil tankers – two Saudi-flagged, one Norwegian-flagged and one Emirati-flagged – were damaged by explosions in waters off the United Arab Emirates.

A UAE-led inquiry published on 7 June found it was “highly likely” that four limpet mines, which are magnetically attached to a ship’s hull under the waterline, were used in the attacks. The report said they had been placed by trained divers deployed from fast boats. The mines were placed soon after the ships were anchored.

The inquiry blamed an unidentified state actor. The US has accused Iran of responsibility, but Iran denies involvement.

Facebook Twitter Pinterest Underwater damage to the four tankers hit by explosions in waters off the UAE on 12 May. Photograph: Reuters

How are countries in the region aligned?

Rivalry between Iran and Saudi Arabia dominates, and the two are engaged in a series of proxy wars across the region, most notably in Yemen.

The US, which backs Saudi Arabia regionally, has 10,000 military personnel stationed at a base in Qatar. The US navy’s 5th Fleet, which assisted in rescue operations on 13 June, is based in Bahrain.

How are US-Iran relations?

Tensions between the US and Iran have soared in recent weeks, with Washington dispatching warships and bombers around the Gulf, and Tehran threatening to resume higher uranium enrichment. A year ago, Donald Trump announced his decision to withdraw from Iran’s 2015 nuclear accord with world powers and restore crippling sanctions.

Timeline Recent tensions in the Gulf Show Hide Tensions between the US and Iran have soared in 2019, with Washington dispatching warships to the Gulf, and Tehran resuming higher uranium enrichment. The UAE says four commercial ships off its eastern coast 'were subjected to sabotage operations'. Yemen's Houthi rebels launch a drone attack on Saudi Arabia, striking a major oil pipeline and taking it out of service. Saudi Arabia subsequently blames Iran for the attack. A rocket lands near the US embassy in the Iraqi capital, Baghdad, without harming anyone. It's not clear who is behind the attack, but after the initial reports, Donald Trump tweets: 'If Iran wants to fight, that will be the official end of Iran. Never threaten the United States again!' Saudi Arabia says 26 people were wounded in an attack by Yemen's Houthi rebels on an airport in the kingdom's south-western town of Abha. Two oil tankers near the strategic strait of Hormuz were reportedly attacked in an assault that left one ablaze and adrift. 44 sailors were evacuated from both vessels and the US navy assisted. Iran’s Revolutionary Guards say they have shot down what they called a US 'spy' drone they claim was flying in in the country’s airspace. The US military confirm one of its drones has been taken down, but say it was in international airspace. Donald Trump reportedly gives approval for the US military to launch strikes on Iran in retaliation for the loss of the drone, before pulling back at the last minute. The Iranian and US presidents trade insults, with Hassan Rouhani suggesting that Donald Trump suffered from a “mental disorder” and Trump once more threatening Iran with “obliteration”. Iran summons UK ambassador over an incident off Gibraltar as Royal Marines seize a tanker, Grace 1, the UK suspects of carrying oil to Syria. The International Atomic Energy Agency, the body tasked with verifying Iranian compliance with the terms of the nuclear deal, verifies that Tehran has breached the agreed 3.67% limit for enriched uranium. The UK government says three Iranian boats were warned off by the frigate HMS Montrose after Iranian boats 'attempted to impede' a British oil tanker in strait of Hormuz. Tehran denies involvement. In a major escalation, Iran seizes the Stena Impero, a British-flagged tanker, off its coast. Iranian officials later make it clear that the capture was in retaliation for the capture of the Iranian supertanker Grace 1 earlier in July. Despite US attempts in the courts to prevent it, Gibraltar says it will free oil tanker at centre of the Iran row. Iran gives assurances the oil is not destined for Syria, where selling it would breach international sanctions against Britain accuses Iran of breaching those assurances after Tehran acknowledged the oil had been sold, and the reflagged tanker Adrian Darya 1, previously known as Grace 1, had reached its final destination after the ship was photographed off the coast of Syria.

Facebook Twitter Pinterest The US aircraft carrier Abraham Lincoln is refuelled. It moved to the Middle East from the Mediterranean last month. Photograph: Mcsn Jason Waite/AFP/Getty Images

What is the role of the strait of Hormuz in the global economy?

The strait, which provides passage from the Gulf of Oman to the open sea, is the most important gateway for oil exports in the world. The US Energy Information Administration (EIA) calls it the world’s worst “chokepoint”, worse than the strait of Malacca, which runs between the Indonesian island of Sumatra, Malaysia and Thailand, connecting the Indian Ocean with the South China Sea. In 2016, 18.5m barrels of crude oil were transported each day through the strait of Hormuz compared with 16m through the strait of Malacca and 5m through the next largest, the Suez canal.

Iran has threatened to disrupt oil shipments through the strait if the US tries to strangle its economy.

Read more about the global economic impact of the attacks.

• This article was amended on 14 June 2019. An earlier version said that in 2016, 18.5m barrels of crude oil were transported through the strait of Hormuz, 16m through the strait of Malacca and 5m through the Suez canal. Those were daily figures, not the total for the year. This has been been corrected.