The clinic where Joan Rivers stopped breathing is "under investigation", a health official confirmed.
Rivers suffered cardiac arrest following a routine operation on her throat at the Yorkville Endoscopy clinic in New York last week and was placed on a life support machine. Earlier this week, she was moved to a private room in intensive care.
The New York medical examiner office "will be investigating the death of Joan Rivers", spokeswoman Julie Bolcer told CNN.
New York State Department of Health representative James O'Hara added that the organisation is "investigating the matter".
Her daughter, Melissa, announced the death, in a New York hospital, in a short statement in which she said: "It is with great sadness that I announce the death of my mother, Joan Rivers.
"She passed peacefully at 1.17pm surrounded by family and close friends. My son and I would like to thank the doctors, nurses, and staff of Mount Sinai Hospital for the amazing care they provided for my mother.
"My mother's greatest joy in life was to make people laugh," she continued.
"Although that is difficult to do right now, I know her final wish would be that we return to laughing soon."
Numerous high-profile names have paid tribute to the comedienne, who was known for her acerbic tongue and wit, including Kelly Osbourne, Lena Dunham, Sarah Silverman and Wu-Tang Clan.
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