(CNN) -- U.S. Air Force officials called off their response late Friday afternoon at a Tucson, Arizona, base after reports that an armed man had entered an office building, the U.S. military branch said in a statement.





Earlier in the day, a U.S. military official told CNN that a gunman was believed to be holed up in a building at the Davis-Monthan Air Force Base.





This precipitated the Air Force to call for a lock-down -- which began at 10:30 a.m. -- "following the unconfirmed sighting of" such a man.





No shots were ever fired and law enforcement teams are on site, said the official, who had direct knowledge of the situation from conversations with base officials but did not want to be identified.





In fact, at 6 p.m., Col. John Cherrey -- who commands the Air Force's 355th Fighter Wing -- told reporters that no gunman or weapon was ever found. He added that the building, where the gunman was once thought to have entered, has been secured after authorities went through it room-by-room.





The announcement came about two hours after the Air Force stated that its officials had "terminated" their response to the incident. All base personnel were leaving via a "controlled release."





"With the help of the Tucson emergency services communities, Airmen were successful in maintaining the safety and security of the Desert Lightning Team," the Air Force said, alluding to the name used for Air Force personnel based in the arid southern Arizona locale.





Earlier, Tucson Police Sgt. Maria Hawke said in an e-mailed statement that members of the department's SWAT team, hostage unit and bomb squad are near the site on a "stand-by" basis in case they are needed. But she said that they are "not actively engaged in any enforcement, investigative or other activity."





And Manuel Johnson, a Phoenix-based spokesman for the FBI, added that some agency personnel have been dispatched to the base to help, if needed.





Shortly before noon Friday, Staff Sgt. Caitlyn Jones confirmed that there was a security situation at the base and that it was on lock-down mode.





"It has been reduced to a single point of entry," she said.





Borman Elementary School, which is located inside the base, was put on lock down at 11 a.m., said Karen Bynum, executive assistant to the Tucson school district's superintendent. Its 501 students were confined to their classrooms, with all perimeter doors locked.





But shortly after 4 p.m., off-base parents were allowed onto the base to pick up students at the school and Sonoran Science Academy, according to a statement from the Air Force. On-base parents were told to "take the most direct route" to locations where their children may be.





The incident occurs nearly two years after 13 people were killed in a shooting spree at the Fort Hood army base in Texas.





CNN's Barbara Starr, Terry Frieden, Tina Burnside and Alta Spells contributed to this report.
When was the lockdown initiated? Who say no gunman was found? Who was dispatched? What was lock down for? Were shots fired? What was the lockdown for? What does the Air Force say?
10:30 a.m. Col. John Cherrey agency personnel "following the unconfirmed sighting of" such a man. No an armed man had entered an office building, called off their response late Friday afternoon
question: When was the lockdown initiated?, answer: 10:30 a.m. | question: Who say no gunman was found?, answer: Col. John Cherrey | question: Who was dispatched?, answer: agency personnel | question: What was lock down for?, answer: "following the unconfirmed sighting of" such a man. | question: Were shots fired?, answer: No | question: What was the lockdown for?, answer: an armed man had entered an office building, | question: What does the Air Force say?, answer: called off their response late Friday afternoon