The Republic | azcentral.com

Authorities on Monday afternoon were still trying to locate the source of the gunshot sounds that prompted officials to lock down Davis-Monthan Air Force Base in Tucson for nearly two hours.

The base's official Twitter account posted a statement at about 10:15 a.m. Monday that said people should take shelter immediately. About 11:40 a.m., an "all clear" was announced on Davis-Monthan's social media accounts.

Monday afternoon, Davis-Monthan issued a statement saying the initial report was made at 9:51 a.m. by someone who said they heard gunshots near the flight line of the base.

Base officials first placed Child Development Centers and on-base schools on lockdown, and security forces completed their sweep of the entire area by 11:38 a.m., the statement said. The lockdown was lifted shortly after.

Officials did not immediately account for what transpired.

Tucson Police Chief Chris Magnus and Pima County Sheriff Mark Napier told the Arizona Daily Star that their departments had been in communication with the base, but neither received requests for support.

"My department has not been requested for support, and we have no people on the ground yet," Napier told the Star.

Napier emphasized to the Star that early information about such incidents can "prove to be inaccurate."

The Tucson Unified School District tweeted that students at its school on base, Borman K-8, were safe.

Sonoran Science Academy, also located on base, sent a tweet shortly before the lockdown was lifted that all students and staff had been accounted for and were safe.

The Arizona Daily Star contributed to this report. Check back with azcentral.com for more details.