In recent weeks, the beverage industry trade group has financed a new coalition led by Alex Azar, an appointee of former President Donald J. Trump, and Donna Shalala, an appointee of former President Bill Clinton. Both Mr. Azar and Ms. Shalala were former secretaries of the Department of Health and Human Services. In an opinion article in Newsweek earlier this month, the two embraced the F.D.A.’s position on the safety of aspartame, and called the agency “the world’s gold standard for independent regulatory bodies.”

The trade group had previously contested another review of aspartame’s potential links to cancer in California. In 2016, a state committee discussed reviewing aspartame, but it went no further.

California officials said this week that the state could review the latest W.H.O. decision.

Besides aspartame, the W.H.O.’s cancer agency has deemed other possible carcinogens to range from the seemingly benign, like Ginkgo biloba extract and aloe vera leaf extract, to the more concerning, like gasoline exhaust and perfluorooctanoic acid, the most common of the industrial chemicals known as per- and polyfluoroalkyl substances, or PFAS, that has recently been subject to billion-dollar settlements over drinking water contamination.

In deeming aspartame a possible carcinogen, the I.A.R.C. also dipped into one of the central controversies of aspartame research. It concluded that there was some evidence for cancer in lab animals based on studies performed by the Ramazzini Institute in Italy, citing the group’s finding of increased tumors in aspartame studies from the mid-2000s. Based on concerns over the group’s methods and interpretations, though, the findings were deemed limited.

For its part, the Ramazzini Institute said in 2021 that its work on aspartame was validated and that its earlier findings were “savagely attacked by the chemical manufacturing and processed food industries and by their allies in regulatory agencies.”

Dr. Branca of the W.H.O. responded to questions about the need for an I.A.R.C. review during a news conference on Wednesday, saying that 10 million people die of cancer each year. “So there’s a societal concern that our organization needed to respond to,” he said.

He said the results demonstrated a clear need for further high-quality research.

“We’ve in a sense raised a flag here, indicating that we need to clarify much more in the situation,” Dr. Branca said. “It is not something which we can dismiss at this moment.”

Julie Creswell contributed reporting to this article.