'Six oil tankers and a United States spy drone have been attacked since May in or near the Strait of Hormuz, which has been described as the world’s most important oil choke point.Tankers carry about 18 million barrels of oil per day — or about 20 percent of global oil demand — through the strait, which separates Iran, Oman and the United Arab Emirates. Most of the oil exported by Gulf countries is shipped through the narrow waterway. The series of attacks has escalated tensions between the United States and Iran. The United States has blamed Iran for the attacks and nearly launched a retaliatory strike on Thursday.Iran denied it had been behind the naval attacks, but said it had shot down the United States’ drone after it had violated Iranian airspace. The United States said the drone had been over international waters.'