Former Maryland governor Martin O'Malley announces his intention to seek the Democratic presidential nomination during a speech on May 30. (Photo by Jim Bourg/Reuters.)

Democratic presidential hopeful Martin O’Malley said that he would prefer there were no super PACs when asked in a radio interview Tuesday about one backing him that recently produced Web ads attacking rival Bernie Sanders.

“Once you’re a candidate, you’re in a bit of a straight jacket,” O’Malley, the former Maryland governor, said during an interview with New Hampshire Public Radio’s Morning Edition. "I would hope that we would keep this debate a debate about the issues, and I would prefer, not that I'm able to tell a super PAC what to do, I would prefer that we didn't have any super PACs, frankly.”

[A pro-O’Malley super PAC goes after Sanders on guns]

The ads in question, produced by the group Generation Forward, attacked Sanders, a Vermont senator, for his mixed record on gun control, asserting that he is “no progressive” on that issue. The ads were targeted to Web viewers in Iowa, the nation’s first presidential caucus state.

Generation Forward is run by allies of O’Malley, including a family friend and a former press aide. Federal law limits coordination between declared candidates and independent groups set up to work for their election. Super PACs, which can take unlimited contributions, have flourished in the wake of the 2010 Supreme Court decision known as Citizens United.

Sanders has urged his allies not to form a super PAC and is one of the few 2016 presidential candidates without one.

[In Iowa, Sanders, O’Malley race to be the Clinton alternative]

In recent weeks, Sanders has jumped in the polls in both Iowa and New Hampshire, emerging as the leading alternative to Democratic frontrunner Hillary Rodham Clinton, while O’Malley’s campaign has remained stalled in the low single digits.

During the radio interview that aired Tuesday, O’Malley also elaborated on his characterization of Sanders last week as a “protest candidate” in an interview with The Washington Post.

[Sanders seen as a ‘protest candidate,’ says Democratic rival O’Malley]

“History has shown usually the candidates that are surging in the summer are not the candidates who are surging in the primary,” O’Malley said.

He made his comments in advance of a planned trip Wednesday and Thursday to New Hampshire, the nation’s first presidential primary state. O’Malley has appearances scheduled in Manchester, Derry, Concord and Wolfeboro.