The No. 2 officer at the military command in charge of all U.S. nuclear war-fighting forces has been suspended and is under investigation by the Naval Criminal Investigation Command for issues related to gambling, officials said Saturday.

The highly unusual action against a high-ranking officer at U.S. Strategic Command was made more than three weeks ago but not publicly announced.

Air Force Gen. Robert Kehler, who heads Strategic Command, suspended the deputy commander, Navy Vice Adm. Tim Giardina, from his duties on Sept. 3, according to the command's top spokeswoman, Navy Capt. Pamela Kunze. Giardina is still assigned to the command but is prohibited from performing duties related to nuclear weapons and other issues requiring a security clearance, she said.

Kehler has recommended to Defense Secretary Chuck Hagel that Giardina be reassigned, Kunze said. Giardina has been the deputy commander of Strategic Command since December 2011. He is a career submarine officer and prior to starting his assignment there was the deputy commander and chief of staff at U.S. Pacific Fleet.

Two senior U.S. officials familiar with the investigation said it is related to gambling issues. The officials spoke on condition of anonymity because the probe in incomplete.

Strategic Command oversees the military's nuclear fighter units, including the Navy's nuclear-armed submarines and the Air Force's nuclear bombers and nuclear land-based missiles. It is located near Omaha, Neb.

Kunze said Strategic Command did not announce the Sept. 3 suspension because Giardina remains under investigation and action on Kehler's recommendation that Giardina be reassigned is pending. The suspension was first reported by the Omaha World-Herald.

The spokeswoman said a law enforcement agency, which she would not identify, began an investigation of Giardina on June 16. Kehler became aware of this on July 16, and the following day he asked the Naval Criminal Investigation Service to begin a probe.