Ad highlights Obama's nonproliferation bill

A new campaign ad airing in Nevada and other states highlights Democratic presidential candidate Barack Obama's work to reduce the threat from nuclear weapons smuggling.

The 30-second television spot begins with Obama standing and addressing a town-hall audience. "We are a beacon of light around the world," Obama says. "At least that's what we can be again. That's what we should be again."

The ad then shows Obama addressing the camera, saying, "The single most important national security threat we face is nuclear weapons falling into the hands of terrorists." An image comes onscreen of bearded men with a stash of weapons, including rockets.

Obama touts his work with Sen. Richard Lugar, R-Ind., "to help lock down loose nuclear weapons," a reference to nonproliferation legislation the two co-sponsored that passed last year.

The campaign said the ad would air in Nevada and 17 other states selected as top battlegrounds, alongside a previously released ad about the dignity of work.

Obama's Republican opponent, John McCain, criticized him Tuesday for presenting a strategy for dealing with Iraq and Afghanistan ahead of a planned trip to those countries, rather than after such a visit.

McCain also has been airing TV commercials in Nevada. The most recent pays tribute to Hispanics in the military.