U.S. Naval Carrier Strike Group Arrives In Arabian Sea As Tensions Rise With Iran A new aircraft carrier strike group has entered the Arabian Sea and another is on its way, a Pentagon official said in a news briefing Wednesday -- a shuffling of the U.S. fleet amid rising tensions with Iran. Officials said there is no connection between the fleet movements and threats from Iran, however, the arrival of the USS Carl Vinson comes on the heals of Iranian military exercises in the Persian Gulf and threats to block the Strait of Hormuz, a major oil transit route. And the killing of an Iranian nuclear scientist in Tehran on Wednesday further escalated tensions, as the Obama administration denied any role in the death. The U.S. Navy announced Monday that the USS Vinson had arrived in the region to conduct missions in support of Operation Enduring Freedom, maritime security operations and theater security cooperation efforts. "We will work closely with our regional partners to demonstrate our commitment to security and stability in the region," Rear Admiral Thomas Shannon said in a written statement. Captain John Kirby, deputy assistant secretary of Defense for Media Operations, on Wednesday denied U.S. involvement in the killing of the Iranian scientist and said the incident has not changed the U.S. position in the Gulf region. And the number of carriers in the region "does go up and down, but it's based on overall broad requirements in the region that the Central Command commander sets and establishes, [it's] not necessarily ... driven by a specific incident," Capt. Kirby said. The shift in naval assets in the region, Kirby said, is not linked to Iran's recent threat to close the Strait of Hormuz, a threat made in response to the West's sanctions on Iranian oil exports over the country's contested nuclear program. The strait is an international waterway, Capt. Kirby said, and the U.S. Navy will continue to be a force in the region "to protect the free flow of commerce in international waters." The Vinson is replacing the outgoing John Stennis Carrier Group, which Iran warned not to return to the gulf last week. But the Vinson's deployment has been long-standing and is not a buildup of force in the region, Kirby said, adding there was nothing usual about this. "[Naval presence in the region] fluctuates based on needs and requirements set by the combatant commander and approved by the Joint Staff and the secretary of defense," Kirby said. To get an aircraft carrier strike group anywhere in the world takes time. It takes a lot of planning and training. Months of advance work is done. In addition to Wednesday's assassination of scientist Mostafa Ahmadi Roshan, tensions between the U.S. and Iran have been fueled by Iran's death sentence for a jailed U.S. citizen on espionage charges, an alleged expansion of Iran's nuclear facilities and threats to bar U.S. ships from the Persian Gulf. Secretary of State Hillary Clinton, speaking beside Qatar's visiting prime minister, on Wednesday criticized Iran over a series of "provocative and dangerous" threats to close the Strait of Hormuz. The United States and others are committed to keeping it open. It's part of the lifeline that keeps oil and gas moving around the world," she told reporters in Washington.