Facebook Inc. and Alphabet Inc.'s Google have little choice but to rein in internet political ads in the face of growing U.S. government pressure, a panel of advertising consultants and executives said on Monday.

Speaking at a trade conference, the marketers seized on allegations that Russian operatives bought U.S. political ads on Facebook as evidence that the sector cannot go on being unregulated.

"I think there will be more scrutiny, and there better be more self-regulation. Otherwise, I think regulation will be coming," Brent McGoldrick, a political ad consultant and a Republican, said at Advertising Week New York.