WASHINGTON, Sept 22 - The United States and partner nations are carrying out the first air strikes against Islamic State targets in Syria, the Pentagon said on Monday, in ongoing operations that mark the opening of a new, far more complicated front in a battle against the militants. "I can confirm that U.S. military and partner nation forces are undertaking military action against (Islamic State) terrorists in Syria using a mix of fighter, bomber and Tomahawk Land Attack Missiles," Rear Admiral John Kirby, Pentagon press secretary, said in a statement. "Given that these operations are ongoing, we are not in a position to provide additional details at this time." Kirby did not disclose which nations joined the United States, which has been building a coalition to combat an extremist Sunni Muslim force that has seized large expanses of territory in Iraq and Syria and proclaimed a caliphate erasing borders in the heart of the Middle East. But a U.S. official, speaking on condition of anonymity, told Reuters there were Arab partners helping to carry out the strikes. Still, the official declined to specify their roles or name the countries. The strikes took place hours before Obama goes to New York for the U.N. General Assembly where he will try to rally more nations behind his drive to aggressively take on Islamic State. "We will provide Obama had shied away from getting involved in Syria's civil war a year ago, seeing no positive outcome for the United States, but the rise of Islamic State and the beheading of two American captives forced him to change course. General Lloyd Austin, commander of the U.S. military's Central Command, made the decision to conduct the strikes under authorization granted to him by Obama, Kirby said. "We will provide more details later as operationally appropriate," Kirby said.