WASHINGTON -- Democratic White House front-runner Barack Obama on Monday told political foes to "lay off my wife" amid signs she could be a target for Republicans in a general election campaign.

The Illinois senator spoke out following the airing of a campaign ad by the Tennessee Republican Party, which used a remark Michelle Obama made earlier this year to question her patriotism.

"If they think that they're going to try to make Michelle an issue in this campaign, they should be careful, because that I find unacceptable, the notion that you start attacking my wife or my family," Obama told ABC television.

"These folks should lay off my wife."

Obama said his wife was the most honest person he knew, and "loves this country," and described the ad as "low class."

The campaign ad, posted on YouTube, repeatedly featured a remark by Michelle Obama that "for the first time in my adult life, I am proud of my country."

It juxtaposes her comment with video of Americans from various states, relating why they are "proud" of the United States.

Michelle Obama said in the interview that she believed Americans would not be diverted by the kind of campaign tactics featured in the ad.

"We're trusting that the American voters are ready to talk about the issues and not talking about the things that have nothing to do with making people's lives better," she said.

Obama has a large lead over fellow Democrat Hillary Clinton in the party's gruelling nominating contests, with the next two primaries in Kentucky and Oregon on Tuesday.

Only five nominating contests remain in total, and Obama, and Republican presumptive nominee John McCain are increasing their attacks on one another in anticipation of a possible general election showdown.