Unexplained damage to a Japanese oil tanker in the Strait of Hormuz in July 2010 is likely to have been caused by explosives, but whether it was an attack could not be determined, the Japanese Transport Ministry said December 27. The incident, in which the shipÃ¢??s hull was dented, has been shrouded in mystery and raised concern about security in the strait, a vital oil shipping lane guarded by U.S. and other warships that handles 40 percent of the worldÃ¢??s seaborne oil. The U.S. Department of Transportation Maritime Administration said in November that militants staged an attack on the tanker, countering speculation it was some kind of accidental collision. Explosives are likely to have gone off outside the ship, the M. Star, above the surface of the water, though no traces had been detected, the ministry said in a report. Checks of the tankerÃ¢??s radar showed some small vessels moving unnaturally in the direction the tanker was heading before it suffered the damage, but no evidence had been found to link the damage to the vessels, the report showed. A U.S. advisory last month described as Ã¢??validÃ¢?? a claim of responsibility by the shadowy Abdullah Azzam Brigades for the failed attack on the M. Star, which injured a seaman lightly but caused no oil spill or disruption. The strike, if confirmed, would be the first such attack in the Strait of Hormuz, but some military experts in the Gulf have expressed skepticism about whether it really was an attack.