WASHINGTON (AP) — The U.S. and Arab allies launched what leaders declared would be a long and sustained military assault against Islamic State strongholds in Syria and Iraq, and the U.S. simultaneously targeted an al-Qaida cell said to be plotting imminent attacks on American and other Western interests, the Pentagon said Tuesday.Hours after the barrage of airstrikes began, Lt. Gen. William Mayville said the attacks took out key Islamic State training camps and facilities. But he said it was too early to tell if they were able to disrupt a terrorist attack being planned by al-Qaida militants, known as the Khorasan Group. He said the group was “nearing the execution phase” of an attack against Europe or the U.S.President Barack Obama said Arab support for the airstrikes “makes it clear to the world this is not America’s fight alone.”“We’re going to do what’s necessary to take the fight to this terrorist group, for the security of the country and the regime and for the entire world,” Obama said as he left Washington for meetings of the U.N. General Assembly in New York.Army Gen. Martin Dempsey, the top American military official, said the U.S. and its Arab allies achieved their aim of showing the extremists their attacks will not go unanswered.The U.S. and five Arab nations attacked the Islamic State group’s headquarters in eastern Syria in nighttime raids Monday using land- and sea-based U.S. aircraft as well as Tomahawk cruise missiles launched from two Navy ships in the Red Sea and the northern Persian Gulf.Gen. Mayville, director of operations for the Joint Chiefs of Staff, said at the Pentagon the U.S. carried out the vast majority of the strikes in an operation against the Islamic State group that he said would continue and likely last “in terms of years.”