Naval Base Guam is home to Los Angeles-class attack submarines and the submarine tenders USS Frank Cable and USS Emory S. Land. (Alex Wilson/Stars and Stripes)

Navy investigators are digging into an arson threat that closed the exchange for 1½ hours Tuesday morning at Naval Base Guam, according to a base spokeswoman.

A vendor at the Navy Exchange reported that someone threatened the store by phone at approximately 8 a.m., base spokeswoman Theresa Cepeda told Stars and Stripes by email Wednesday.

She said the Naval Criminal Investigative Service is looking into the threat that prompted security forces to evacuate and search the exchange building.

“Emergency responders were dispatched immediately and the facility was evacuated,” Cepeda said. The commissary was also temporarily closed, a statement on the base’s Facebook page said Tuesday morning.

Navy security forces cordoned off the exchange, the surrounding buildings and roads, Cepeda said. Base authorities used social medial to warn of restricted access to the area and urge store patrons to stay away.

A sweep inside the building by fire and emergency services, followed by a second sweep outside by base security with a K-9, discovered nothing suspicious, she said. The building was declared all clear at 9:15 a.m.

Naval Base Guam is home to Los Angeles-class attack submarines and the submarine tenders USS Frank Cable and USS Emory S. Land.