Kevin Cosgriff, commander of the U.S. 5th Fleet stationed in Bahrain across the Persian Gulf from Iran, warned that such Iranian action would be considered an act of war, and the U.S. would not allow Iran to hold hostage nearly a third of the world's oil supply. On 8 July 2008, Ali Shirazi, a mid-level clerical aide to Iran's Supreme Leader Ayatollah Ali Khamenei, was quoted by the student news agency ISNA as telling the Revolutionary Guards, "The Zionist regime is pressuring White House officials to attack Iran. If they commit such a stupidity, Tel Aviv and U.S. shipping in the Persian Gulf will be Iran's first targets and they will be burned." Naval activity in 2008 In the last week of July 2008, in the Operation Brimstone, dozens of U.S. and foreign naval ships came to undergo joint exercises for possible military activity in the shallow waters off the coast of Iran. As of 11 August 2008, more than 40 U.S. and allied ships reportedly were en route to the Strait of Hormuz. One U.S. carrier battle group from Japan would complement the two which are already in the Persian Gulf, for a total of five battle groups, not including the submarines. Collision between USS Hartford and USS New Orleans On 20 March 2009, United States Navy collided with the in the strait. The collision, which slightly injured 15 sailors aboard Hartford, ruptured a fuel tank aboard New Orleans, spilling of marine diesel fuel. U.S.–Iran tensions in 2011–2012 On 27 December 2011, Iranian Vice President Mohammad-Reza Rahimi threatened to cut off oil supply from the Strait of Hormuz should economic sanctions limit, or cut off, Iranian oil exports. A U.S. Fifth Fleet spokeswoman said in response that the Fleet was "always ready to counter malevolent actions", whilst Admiral Habibollah Sayyari of the Islamic Republic of Iran Navy claimed that cutting off oil shipments would be "easy". Despite an initial 2% rise in oil prices, oil markets ultimately did not react significantly to the Iranian threat, with oil analyst Thorbjoern Bak Jensen of Global Risk Management concluding that "they cannot stop the flow for a longer period due to the amount of U.S. hardware in the area". On 3 January 2012, Iran threatened to take action if the U.S. Navy moves an aircraft carrier back into the Persian Gulf. Iranian Army chief Ataollah Salehi said the United States had moved