An attack struck the U.S.-flagged oil tanker Stena Imperative while it was docked in Bahrain, killing one shipyard worker and injuring two others, according to the vessel’s operator Crowley. The company said the ship “suffered damage due to aerial impacts,” and a fire onboard was extinguished quickly. Crowley added that the vessel’s American mariners reported no injuries.

Crowley said the incident occurred shortly after 2 a.m. local time. The tanker was in a dry dock at Khalifa bin Salman Port at the time, according to ship-tracking firm Kpler. The operator said it was not clear who carried out the attack.

Stena Imperative is part of a fleet of roughly 10 commercial tankers that can be called on to support the U.S. military in times of conflict. However, a Crowley spokesperson said the ship was in Bahrain for planned maintenance and regulatory-required inspections, and it had no fuel cargo.

The report said regional risks to commercial shipping have increased as U.S. and Israeli airstrikes and subsequent retaliatory attacks have unfolded around the Persian Gulf. It also said the tanker had previously been intercepted by Iranian gunboats as it entered the Gulf through the Strait of Hormuz, based on an account from maritime risk broker Vanguard Tech.

The report further said at least five other oil tankers have been attacked since that episode, citing analysis based on satellite imagery, maritime reports, ship-tracking data and official statements. It also said Iran’s Revolutionary Guards Corps claimed responsibility for three attacks, according to Iran’s semiofficial Mehr News Agency.