Clinton Campaign Accuses Bernie Sanders of Breaking Pledge Not to Go 'Negative'

NEW YORK -- The feud between the Hillary Clinton and Bernie Sanders campaigns is escalating.

One day after Clinton went after Sanders for his health care plan, her campaign on Thursday accused the Vermont senator of going “negative” in a new ad that appears to draw a contrast between the two Democratic presidential candidates on their views about Wall Street.

Sanders, however, denies the ad —- which does not mention Clinton by name —- is about her.

The ad in question is titled “Two Visions” and was released earlier today for air in Iowa and New Hampshire.

In the ad, Sanders says: "There are two Democratic visions for regulating Wall Street. One says it's okay to take millions from big banks and then tell them what to do. My plan: break up the big banks, close the tax loopholes, and make them pay their fair share.”

The Clinton campaign held an abruptly scheduled conference call with reporters this afternoon to respond to the ad.

“We were very surprised today to see that Bernie Sanders had launched a negative television advertisement against Hillary,” Clinton campaign manager Robby Mook said.

“This ad does something that Bernie said he wouldn’t do,” campaign pollster Joel Benenson added, referring to how the Vermont Senator has said he will not run negative campaign ads.

During a press conference tonight, Sanders denied the Clinton campaign's assertion that this line was an attack on Clinton.

“This is not a negative ad," Sanders said, “Everybody knows that there are two visions within the Democratic Party. There is the vision with those people who fought to deregulate Wall Street, who are very tight with Wall Street, and those who fought very hard against that deregulation and want to break up the banks. That is what that ad says. And it clear which side I am on."

Sanders also pointed to an ad Clinton released earlier this week in which she appears to draw a contrast with the Vermont senator on guns. "It's time to pick a side," Clinton says about the gun control debate.

During the conference call, the Clinton campaign denied the gun ad was going after Sanders, but also did not rule out the possibility of launching negative ads against him in the future.

"I think we will wait and see what Senator Sanders does,” Benenson said.

The back-and-forth between the two candidates comes the same week new polls show Sanders gaining on Clinton in the polls, including a Quinnipiac poll of Iowa that has Sanders with a 5 point lead.

ABC News' MaryAlice Parks contributed to this report.