UniQure needs to run another study to prove that its gene therapy “actually helps people with Huntington’s disease,” a senior U.S. Food and Drug Administration official said on a call with reporters Thursday.

The official, who requested anonymity before discussing sensitive information, confirmed the agency has asked the company to run a placebo controlled trial of its treatment, which is administered directly into the brain. UniQure has said that type of study isn’t ethical because it would require putting people under general anesthesia for hours, a characterization the official disputed.

“So what is really going on? UniQure is the latest company to make a failed therapy for Huntington’s patients,” the official said. “They likely acknowledge or understand at some deep level that their trial failed years ago, and instead of doing the right thing and running the correct clinical study, UniQure is performing a distorted or manipulated comparison in the mind of FDA.”

The comments mark the latest development in a messy public spat between UniQure and the FDA, and as the agency comes under fire for a number of recent drug approval application rejections, including some where companies have accused it of going back on previous guidance. FDA Commissioner Marty Makary in an interview with CNBC’s Becky Quick last week seemingly criticized UniQure’s gene therapy for Huntington’s disease. Makary didn’t name UniQure but described its treatment.

UniQure then accused the FDA of reversing its stance that the company’s clinical trial data would be sufficient to seek approval. UniQure’s study used an outside database to measure how patients with Huntington’s disease might decline without treatment, known as an external control. UniQure has said it wouldn’t be feasible to run a true randomized, double-blind placebo-controlled study, considered the gold standard, because it wouldn’t be ethical to make people undergo a sham hours-long brain surgery.

The FDA official said the agency “never agreed to accept this distorted comparison” and the FDA “never makes such assurances.” Instead, the “FDA will always say, ‘Well, we have to see the data when we get it.'”

UniQure didn’t immediately comment.

The company’s stock rose more than 10% on Thursday and has fallen 58% this year as of Thursday afternoon.