The US military has advised its staff to treat armed civilians standing guard outside its recruiting centres as a security threat.
The groups started appearing outside military offices in various states after a gunman killed five service members at a Tennessee Navy facility.
Some have argued that the deaths could have been prevented if the recruiters had been armed.
Typically military recruiters do not carry weapons.
Mohammad Youssuf Abdulazeez, 24, opened fire on a recruitment centre on 16 July in Chattanooga. He then drove about six miles (10km) to a Navy and Marine reserve centre, where he shot and killed four marines and one sailor.
Some military personnel were armed at the second location.
“The citizens mean well, but we cannot assume this in every case, and we do not want to advocate this behaviour,” the Army said in a statement.
The statement instructs military staff to be polite but to avoid contact with the armed men.
The military has maintained that the presence of weapons at recruiting stations are more trouble than they are worth.
The military and local law enforcement ordered a group of armed men to leave an office on Thursday in Lancaster, Ohio, after one of the men accidently discharged his AR-15 rifle.