LAS VEGAS — A National Rifle Association-backed group has begun airing a TV ad featuring the Nevada state attorney general and three sheriffs urging voters to reject a gun-purchase background checks measure on the November statewide ballot.

The 30-second spot by NRA Nevadans for Freedom debuted Tuesday, featuring Attorney General Adam Laxalt and sheriffs Ken Furlong of Carson City, Chuck Allen of Washoe County and Gerald Antinoro of Storey County. They say the measure wouldn’t prevent crime and would criminalize gun ownership.

The ad says the fight is really about gun control and urges voters to “stand with law enforcement” against the measure, Question 1.

Nevadans for Background Checks, proponents of the measure, began airing an ad two weeks ago featuring another law-enforcement official, Nevada Association of Public Safety Officers President Jim Dunlap. It says approving the initiative would reduce gun violence and save police officers’ lives because it would become harder for criminals to get guns.

The National Rifle Association group responded that criminals would still get guns.

A yes vote on the initiative would require background checks through a licensed gun dealer when most firearms change hands. Exceptions would be made for giving guns to immediate family members, temporary transfers of a weapon while hunting or target shooting, and for immediate self-defense.

In a statement Tuesday, the proponents’ group accused the NRA of using “half-truths” in its ad to scare legal gun owners into thinking the measure threatens Second Amendment rights.

The NRA-backed opponents criticize the proponent group for accepting financial backing from Everytown for Gun Safety Action Fund, a group affiliated with former New York City Mayor Michael Bloomberg.