A US air force base was put on lockdown for nearly five hours  after a report suggested a gunman was holed up inside the facility, but it turned out to be a false alarm, officials said. All traffic in and out of the Davis Monthan air base in Tucson, Arizona, was stopped after the "reported sighting of an armed individual entering an office building," said a base statement. A SWAT team and bomb squad were scrambled to the scene, local media said, while at least one nearby school was also on lockdown. "The base remained in lockdown from approximately 10:30 am until approximately 4:00 pm when a floor-by-floor, room-by-room search of the building in question was completed," said the statement. "Local and federal law enforcement personnel in concert with base security forces conducted a sweep and secured the building, where the alleged gunman was reported. But it said: "No gunman or weapons were found. The building was declared secure and an orderly release of personnel followed." And it added. "All reports of threats regarding the safety and security of our Airmen and their families are taken seriously. The base is home to the 355th Wing, which provides attack air power, combat support and medical forces ready for worldwide deployment to combatant commanders, according to its website. Security across the United States has been tightened in recent weeks due to the 10th anniversary of the September 11, 2001 attacks on New York and Washington.