Governments and tanker companies were stepping up efforts to protect key shipping routes as the US and Iran traded accusations over attacks on two tankers in the Gulf of Oman, a waterway traversed by over a third of the world's seaborne crude oil.
Saudi Arabia has increased security around oil facilities and strategic areas, Efe news reported on Saturday citing a senior Saudi official as saying.
The official said the attacks have exposed vulnerabilities in the Strait of Hormuz, through which between two and three dozen ships pass every day. Gulf states are struggling to mount a strong defence against drones and torpedoes.
"The key thing now is to find a way to deal with those type of attacks in the future and assure everyone that those routes are still safe," the official said.
The United Arab Emirates (UAE) has joined shipping companies to increase sea-lane security in the Persian Gulf, Strait of Hormuz and Gulf of Oman, according to informed Gulf officials.
Shipping insurance costs were rising fast, with rates on super-tanker cargoes for the Middle East-to-China route jumping 34 per cent after the attacks on Thursday, hitting $24,854 a day, according a broker in Singapore.
US officials said that it was clear Iran's Islamic Revolutionary Guard Corps (IRGC) was responsible for the attacks on the Japanese-owned Kokuka Courageous and the Front Altair, owned by a Norwegian company.
"Iran did do it," President Donald Trump said on Fox News, pointing to a video that US Central Command said showed an IRGC vessel removing a limpet mine from the hull of one of the ships, the Kokuka Courageous.
In response to the accusations, Iranian Foreign Minister Javad Zarif on Friday shot back on Twitter, suggesting the US or its allies were likely behind the assaults and that Washington "immediately jumped to make allegations against Iran - (without) a shred of factual or circumstantial evidence".
Persian Gulf oil producers and tanker companies scurried in response to tension "as high as it gets without being an actual armed conflict", according to BIMCO, a shipping trade group.
Military units from unspecified countries are deployed off Fujairah, the eastern-most emirate of the UAE, for "surveillance, monitoring and response", said tanker-industry associations Intertanko and Oil Companies International Marine Forum, or OCIMF.
"It's a difficult situation and there may be more attacks," said Theodore Veniamis, president of the Union of Greek Shipowners, whose members control around a third of the world's crude tankers and 15 per cent of chemical and product tankers.
"The threat to crews and ships is high."
Thursday's attack followed weeks of tension in the region between Iran and the US in the wake of the Trump administration's exit last year from the multinational 2015 nuclear deal and imposition of sanctions on Tehran.
The US and it's Middle East allies have accused Iran of orchestrating a series of attacks in recent weeks, including the sabotage of four tankers in the Gulf of Oman in May and drone attacks by Yemeni Houthi rebels on Saudi Arabia.
Washington has increased its military presence in the region in response to what it calls Iranian threats, while Tehran has threatened to withdraw from some limits on its nuclear program in retaliation for sanctions.
The Trump administration has said it was considering options including military escorts for tankers travelling through the area, but some US military officials said they don't believe accompanying each tanker through the Strait of Hormuz was practical.
Meanwhile, analysts have said that if Iran was responsible for the attacks, they were likely carried out by the IRGC, a powerful military cadre that answers only to Supreme Leader Ayatollah Ali Khamenei.
IRGC commanders have repeatedly threatened to shut down the Strait of Hormuz if Iran isn't allowed to export oil. Under US sanctions, Iranian oil exports have fallen to about 500,000 barrels a day, down from 2.9 million barrels a day in 2016.
The IRGC hasn't publicly commented on the attacks, but Iran's mission to the UN in a statement on Thursday called the allegations "another Iranophobic campaign".
The details of Thursday's attacks made shipowners nervous.
One of the tankers, a Norwegian vessel, appeared to have been hit by a torpedo. The other tanker, owned by Kokuka Sangyo Co., was struck by two "flying objects".
Shipping trade groups offered advice for captains and crews operating in the region. The Norwegian Maritime Authority advised captains to keep a safe distance from Iranian waters and called for increased patrols, including in ports and on vessels.
BIMCO recommended measures such as increased onboard patrols, notably in non-restricted areas of vessels.
It also advised crews and captains to make sure hulls are well secured by closing doors and hatches that could be entered from the outside, and ensure that crews sleep in areas located above the waterline.
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