NEW YORK  -    US investigators believe Iran or groups it supports used explo­sives to damage four ships off the United Arab Emirates on Sunday, media reports say. Mil­itary experts were reportedly sent to investigate the incident and found a large hole in each of the tankers. No evidence has emerged to show that Iran was involved. The affected coun­tries are yet to assign blame. The incident has increased ten­sions between Iran, which bor­ders the nearby Strait of Hor­muz, and the US. About a fifth of oil that is consumed glob­ally passes through the strait. Last month, Iran threatened to close it if it was prevented from using the waterway. This followed a US decision to end exemptions from sanctions for major importers of Iranian oil. The team of US military inves­tigators discovered large holes in all four of the affected ships and believe they were caused by explosive charges.