A candidate for a US Senate seat has spoken of the need for new gun regulations while assembling an assault rifle blindfolded.

Running as a Democrat in one of the most gun-loving states in the US, Missouri's Jason Kander has already faced repeated attacks from the National Rifle Association (NRA) and his opponent for his support of gun control.

But the former Army Captain and current Missouri Secretary of State has replied with perhaps the best campaign ad of the election.

"In the Army, I learned how to use and respect my rifle ," Kander said while assembling the AR-15 semi-automatic rifle blindfolded.

"I also believe in background checks, so that terrorists can't get their hands on one of these."

Kander then removes his blindfold and calls on his rival, Senator Roy Blunt, to complete the same task.

It is a bold ad, one designed to inoculate Kander from suggestions that he is anti-gun because he is pushing for further regulation.

In the latest poll of the race, Kander has eked out a narrow lead over Blunt, 42 to 40.

The same poll shows Hillary Clinton trailing Donald Trump in Missouri by a hefty 13-point margin.

Kander's ad is not the first from a Missouri candidate intent on burnishing their credentials as gun users.