WASHINGTON — President Barack Obama is challenging Mitt Romney’s promises to crack down on China’s trading practices, saying in an ad released Saturday that the Republican candidate profited by allowing China to strip away U.S. jobs.

Obama’s ad turns again to a recent Washington Post report that several businesses backed by Romney’s former private equity firm moved American jobs to China and India to cut costs. In a parting shot, a narrator says Romney is “not the solution. He’s the problem.”

The ad follows Obama’s two-day bus tour in Ohio and Pennsylvania, where the president announced plans to file a trade complaint against China at the World Trade Organization for unfairly imposing duties on the exports of U.S.-produced automobiles.

China remains a flashpoint in the presidential campaign.

Romney has accused Obama of failing to live up to promises to get tough on the economic powerhouse.

Obama’s administration says it has taken a broad effort to crack down on what it calls unfair Chinese trading practices, filing seven trade cases with the WTO against Beijing.

The 30-second spot opens with a clip of Romney during a 2011 Republican primary debate. He says “the Chinese are smiling all the way to the bank taking our jobs and taking a lot of our future. And I am not willing to let that happen.”

A narrator responds that Romney “made a fortune letting it happen.”

The Obama ad refers to the Post account about the role Romney’s firm played with companies that were “pioneers” in helping outsource jobs. It pointed to one business that said it was a “one-stop shop for their outsource requirements.”

“Mitt Romney’s not the solution. He’s the problem,” the narrator says.

Romney spokeswoman Andrea Saul said it was “no surprise President Obama would want to distract Americans from the devastating June jobs numbers, but the American people deserve better than dishonest ads.”

Romney’s campaign has questioned the accuracy of the report and asked the Post for a retraction. The newspaper stood by its report.