(CNN) -- Joan Rivers' personal throat doctor denies "performing an unauthorized procedure" before the comedian suffered cardiac arrest, a source close to the doctor told CNN.
Dr. Gwen Korovin also "categorically denies" taking a selfie photo of Rivers while she was under anesthesia at a medical clinic, the source said Thursday.
The statement disputes what a source close to the Rivers death investigation told CNN: that staff members at the clinic told investigators that Korovin snapped the selfie while Rivers was under anesthesia and also performed an unauthorized procedure on Rivers.
Rivers, 81, died a week after suffering cardiac arrest during an appointment at Manhattan's Yorkville Endoscopy clinic.
CNN's source close to the investigation also provided new details Thursday, including that Rivers was visible in Korovin's procedure room selfie.
Clinic workers told investigators they heard Korovin make a statement to the effect that Rivers "will think this is funny" or "would love this" as she took the photo, the source said.
Investigators do not have access to the phone Korovin used to take the photo, the source said.
The source also provided more specific information about what procedures were done on Rivers.
Several clinic workers told investigators that it began with Korovin performing a laryngoscopy, which involves using a device to view a patient's vocal folds.
Gastroenterologist Dr. Lawrence Cohen, who was the medical director of the clinic until resigning after Rivers' death, then performed an endoscopy intended to diagnose why she was suffering a sore throat and hoarseness, the source said.
Cohen detected something of concern, the source said.
Korovin then began a second laryngoscopy to again view River's vocal cords, the source said. It was at that time that her vocal cords began to swell, leading to a cutoff of oxygen to her lungs and ultimately to cardiac arrest, according to the source.
The clinic denies published reports that a vocal cord biopsy was performed moments before Rivers went into cardiac arrest.
Paramedics rushed Rivers from Yorkville Endoscopy to New York's Mount Sinai Hospital a mile away, where she was kept on life support until she died a week later.
Korovin was authorized only to observe Cohen, who performed the procedure, since she was not certified by Yorkville Endoscopy clinic, as required by New York health law, the source said.
Investigators have found no prior consent form signed by Rivers authorizing a procedure by Korovin, the source said. It was unclear if Rivers had given verbal consent to the biopsy before being sedated.
Korovin is well known for helping an impressive list of celebrities with voice trouble. The list of famous patients who have sung her praises include actors Hugh Jackman and Nathan Lane and singers Celine Dion, Lady Gaga and Ariana Grande.
The walls of Korovin's Manhattan medical office are covered with autographed photos, including from operatic tenor Luciano Pavarotti, Broadway star Barbara Cook and actress-singer Julie Andrews.
"I've always been fascinated by the human voice and music," Korovin, 55, is quoted telling the New York Daily News in a profile story last year.
Korovin's lawyer sent a statement to CNN on Thursday in response to the reports:
"Gwen S. Korovin, M.D. is a highly experienced, board certified otolaryngologist. She maintains privileges at one of the city's most prestigious hospitals. She is respected and admired by her peers in the medical community and she is revered by her patients.
"As a matter of personal and professional policy, Dr. Korovin does not publicly discuss her patients or their care and treatment. Further, Dr. Korovin is prohibited by state and federal confidentiality laws from discussing her care and treatment of any particular patient.
"For these reasons, neither Dr. Korovin nor her attorneys will have any public comment on recent press reports regarding her practice. We ask that the press please respect Dr. Korovin's personal and professional policy of not discussing her patients, as well as the privacy of her patients."
Accreditation agency makes a visit
The American Association for Accreditation of Ambulatory Surgery Facilities (AAAASF) sent representatives for an unscheduled visit to the clinic after hearing about Rivers' cardiac arrest, according to letters from the group.
The letters cited two "deficiencies" found by the representatives, declared the clinic to be in "immediate jeopardy" and placed it on "emergency suspension." The accreditation group said the clinic should stop procedures and surgeries "until accreditation questions are settled."
The clinic, however, sent CNN a statement Friday acknowledging the visit by the accreditation groups and saying "it is is in the process of implementing those steps" requested by the group.
The clinic's credentialing procedures have been revised after meeting with the accreditation agency's surveyors, it said.
Yorkville Endoscopy is fully operational and under no suspension, the clinic's spokeswoman said.
While the accreditation agency has no power to shut a clinic down, the state of New York does. State health investigators also found deficiencies in Rivers' treatment, according to a source close to the death investigation. These include the participation of Rivers' personal throat doctor.
Yorkville Endoscopy issued a statement last Thursday denying reports that any vocal cord biopsy has ever been done at the clinic, although federal privacy law prevented any patient information from being released.
The day after the denial was issued, the clinic confirmed that Cohen "is not currently performing procedures. ... Nor is he currently serving as medical director."
The source said that at this time, neither Cohen nor the ear, nose and throat doctor have been accused of wrongdoing by investigators.
Melissa Rivers has been silent since her mother's death on September 4, although she did post an online message thanking friends and fans Wednesday evening.
"As my son Cooper and I mourn the loss of my mother, we want to thank everyone for the beautiful cards and flowers conveying heartfelt messages and condolences, which continue to arrive from around the world and through social media. My mother would have been overwhelmed by the scope and depth of the love that people have expressed for her. It is certainly helping to lift our spirits during this time.
"We are forever grateful for your kindness and support in continuing to honor my mother's legacy, and for remembering the joy and laughter that she brought to so many."
CNN's Lena Jakobsson contributed to this report.