COLUMBUS, Ohio -- Gun-toting Americans are showing up at U.S. military recruiting centres around the country, saying they plan to protect recruiters following last week's killing of four Marines and a sailor in Chattanooga, Tennessee.

The citizens said they're supporting the recruiters, who by military directive are not armed. Only law enforcement or military police can have weapons on federal property, which includes recruiting centres.

"We're here to serve and protect," Clint Janney said Tuesday, wearing a Taurus 9mm handgun as he stood in a parking lot across from a recruiting centre in Columbus. "What the government won't do, we will do."

Similar posts have been set up outside recruitment centres in several other cities, including Madison, Wisconsin; Hiram, Georgia; Phoenix; and several sites in Tennessee, including Murfreesboro.

There's no evidence that such centres are in danger, and the government isn't changing how they're staffed, although some governors have temporarily moved National Guard recruiting centres to armouries and several have authorized Guard personnel to carry weapons at state facilities.

Janney, 38, who runs his own garage door company, is a member of the Ohio branch of the "3 Per cent Irregulars" militia. He was joined by four other members of the militia. In Ohio and many other U.S. states, it is legal to carry an openly displayed handgun or rifle.

The men sat in lawn chairs, occasionally dipping into a cooler for bottles of water, or stood around talking. Some people came by to thank them; others didn't seem aware of their presence.

Franklin County Sheriff Zach Scott said as long as the owner of the plaza didn't ask them to leave, the men were not violating any laws.

Employees of a medical supply centre next door to the recruiting centre said they understood the volunteers' intentions but weren't thrilled about their presence. Customers thought professional security guards would be better.

"They could just go crazy with the shooting. You just don't know their state of mind," said Kimm McLaughlin, 44.

On Tuesday, the founder and president of Oath Keepers, a Las Vegas-based Constitution activist group, issued a national call to members to guard centres. Many were already guarding centres in Tennessee, Arkansas and Oklahoma, president Stewart Rhodes said.

Rhodes said it's "absolutely insane" that recruiters aren't allowed to be armed.

"They're sitting ducks," Rhodes said Tuesday. "They'd be better off if they were walking down the streets of Baghdad, because at least in Baghdad, they could move. Here, they're stationary."

Capt. Jim Stenger, a Marine Corps public affairs officer for the recruiting district that includes parts of seven Midwestern states, said he hopes the gun-toting civilians will go home.

"While we greatly appreciate the support of the American public during this tragedy, we ask that citizens do not stand guard at our recruiting offices," Stenger said in a statement.

U.S. Army Recruiting Command spokesman Brian Lepley said, while tragic, deadly incidents have happened only twice in six years at recruiting centres: in Chattanooga last week, and in Little Rock in 2009 in a shooting that killed one solider and injured another.

"Recruiting stations need to be out in the public; we need to be out where young people are," Lepley said. Most recruiters are Afghanistan and Iraq war veterans, well trained in dealing with shooters, he added.

A group of veterans and their supporters began guarding a Navy-Marine recruiting station in Madison, Wisconsin.

"Just civic pride," said David Walters, a 30-year-old Army veteran. "It's good to show that people can still come together."

In Hiram, Georgia, five people stood outside a recruiting office Friday with their personal firearms as a show of support. They had a pop-up tent, a few lawn chairs and American flags, Police Chief Todd Vande Zande said.

"If it makes them feel better as American citizens and they're not doing anything illegal, then I'm all for it," he said.

Associated Press writers Kantele Franko in Columbus, Kate Brumback in Atlanta, Todd Richmond in Madison, Wisconsin, and Jacques Billeaud in Phoenix contributed to this report