JEFFERSON CITY -- Democratic Attorney General Chris Koster announced Monday that the National Rifle Association Political Victory Fund has endorsed his campaign for a second term.

Koster is the only statewide Democrat to earn an "A" rating from the national pro-gun organization, and the only one to receive the group's support.

“I am honored to receive the NRA’s endorsement,” Koster said in a statement. “As attorney general, my job is to protect and defend the rights of all Missourians — and this includes their right to bear arms."

According to the NRA website, an "A" rating means the candidate is "solidly pro-gun" and has "demonstrated record of support on Second Amendment issues."

Koster's Republican challenger, Ed Martin, won the group's endorsement during the Republican primary. He received an "AQ" in the most recent endorsements, which means the rating was based on a questionnaire since Martin has no voting record.

In addition to Koster, the NRA endorsed three Republicans: Lt. Gov. Peter Kinder, secretary of state nominee Shane Schoeller and state Treasurer nominee Cole McNary. The group made no endorsement in the race for governor.

Also on Monday, Martin released his first television ad of the 2012 general election campaign. Koster launched his first ad two weeks ago.