(Reuters) - The National Rifle Association was more deeply involved than previously disclosed in the formation of a movement that encouraged county sheriffs not to enforce some gun-control laws, a U.S. gun-control advocacy group said on Monday, based on public records it obtained.

Under the so-called Second Amendment sanctuary movement, county sheriffs in at least four states have vowed to refuse to enforce laws that they consider to be infringements on the U.S. constitutional right to keep and bear arms.