The Pentagon asked on Friday that concerned armed citizens not stand guard at military recruiting offices, saying it can handle security after a shooting rampage on its own.

Prompted by shootings at military facilities in the US, Americans have started showing up at military recruiting offices to stand guard with handguns and rifles.

Pentagon spokesman Peter Cook said the Defense Department appreciated the "outpouring of support" but warned that the volunteers might do more harm than good.

"We ask that individuals not stand guard at recruiting offices as it could adversely impact our mission, and potentially create unintended security risks," Cook said.

An armed civilian guarding a recruitment center in Ohio accidently discharged his rifle on Thursday, The Columbus Dispatch reported.

Last week, a 24-year-old gunman opened fire at two military facilities in Tennessee, killing four US marines and a sailor.

The shooting renewed a debate over military members being unarmed on US soil. The Tennessee shooter, Mohammad Youssuf Abdulazeez, was killed in a gunfight with civilian police.

Defense Secretary Ashton Carter has promised a review of security measures but the military has resisted arming troops at home.

"We take the safety of our service members, our DoD civilians, and the families who support them very seriously," Cook said.

"Secretary of Defense Ash Carter is currently reviewing recommendations from the services for making our installations and facilities safer -- including our recruiting stations"