(Bloomberg) -- Iranian forces were likely responsible for the attacks that occurred Thursday on two tankers in the Gulf of Oman, according to a report seen by Bloomberg from DNK, the insurer of one of the ships.

The Norwegian insurer has raised its assessment on the threat to tankers in the Persian Gulf, Strait of Hormuz and North Western Gulf of Oman to high following the incident, it said in the report. Anti-ship missiles fired from a naval asset were probably used in the attacks, it said.

The attacks on two tankers on Thursday have stoked regional tensions, with oil tanker owners reluctant to send vessels to the region. The U.S. has said it will consider providing naval escorts for commercial ships travelling through the Strait of Hormuz, the chokepoint at the southern end of the Persian Gulf. The U.S. has blamed Iran for the attacks on both vessels, while Tehran denies the accusations.

Read more on the impact on the shipping industry and insurance premiums

Details on the crew’s evacuation from the Front Altair tanker also emerged in the report from DNK, which insures the vessel. The crew was forced to board an Iranian vessel, having already been picked up by a nearby commercial vessel.

Iran’s navy “demanded that the crew were transferred to them,” DNK said in the circular. The crew was then taken to the Iranian port of Jask.

DNK, formally known as the Norwegian Shipowners’ Mutual War Risks Insurance Association, declined to comment on the report. The explosion on the Front Altair “was caused by a hostile attack,” it said in a statement Friday, without assigning responsibility.

--With assistance from Mikael Holter.

To contact the reporter on this story: Verity Ratcliffe in Dubai at vratcliffe1@bloomberg.net

To contact the editors responsible for this story: Nayla Razzouk at nrazzouk2@bloomberg.net, Rachel Graham, John Deane

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