WASHINGTON (AP) — Democrats are criticizing a TV ad sponsored by a political action committee that opposes Hillary Rodham Clinton's presidential bid. The ad shows the grave of Chris Stevens, the U.S. ambassador killed in Benghazi, Libya.

The 30-second ad by the Stop Hillary PAC aired on CNN in Washington, New York and other media markets during Tuesday's Democratic debate. It also shows photos of Stevens and three other Americans killed during the 2012 attacks on the U.S. diplomatic compound in Benghazi.

Democrats on the House Benghazi committee condemned the ad Wednesday and said Stevens' image was used without his family's permission.

Rep. Elijah Cummings of Maryland, the senior Democrat on the panel, called the ad offensive and shameful. He and other Democrats urged the panel's chairman, Rep. Trey Gowdy, R-S.C., to use his influence to get the ad removed immediately.

Dan Backer, treasurer of the anti-Clinton group, said the ad was designed to "convey as powerful a message as possible" about the tragedy and Clinton's possible role in it. "Four Americans died. They didn't have to, but they did," Backer said.

Jamal Ware, a spokesman for Gowdy, said the ad does not mention either the Benghazi committee or Gowdy, and the committee played no role in the ad.

"The gratuitous demand by Ranking Member Cummings is further proof Democrats do not care about investigating Benghazi, only playing politics like the makers of that ad," Ware said.

Gowdy had previously sent the Stop Hillary group a cease-and-desist letter when they invoked his name.

Wednesday evening, Clinton's campaign pointed out a radio interview in which Rep. Richard Hanna, R-N.Y., said, "There was a big part of this investigation that was designed to go after ... an individual: Hillary Clinton."

Clinton spokesman Brian Fallon said, "House Republicans aren't even shy anymore about admitting that the Benghazi Committee is a partisan farce."

Clinton is scheduled to testify before the committee next week. "Hillary Clinton will still attend next week's hearing," Fallon said, "but at this point, Trey Gowdy's inquiry has zero credibility left."