HOUSTON, Texas (CBS) – A puppy died on a United Airlines flight from Houston to New York Monday after a flight attendant told the dog’s owner to put it in the overhead bin, CBS News reports.

A passenger on the flight told The Points Guy the puppy was in a TSA-approved pet carrier.

According to Chicago-based United’s website, its policy for on-board pets is: “A pet traveling in cabin must be carried in an approved hard-sided or soft-sided kennel. The kennel must fit completely under the seat in front of the customer and remain there at all times.”

However, several passengers reported that flight attendants insisted the family put the puppy in the overhead storage bin during the three-hour flight.

A man named June Mara said he was seated behind the family of three — a mother, a young girl “no older than 8” and a toddler — and their 10-month-old Frenchie “Papacito.” The puppy was a birthday gift.

“…the flight attendants of flight UA1284 felt that the innocent animal was better off crammed inside the overhead container without air and water,” Mara wrote on Facebook. “They INSISTED that the puppy be locked up for three hours without any kind of airflow. They assured the safety of the family’s pet so wearily, the mother agreed.”

Mara said the puppy could be heard crying from the overhead bin during the first part of the flight — and then he went silent.

“There was no sound as we landed and opened his kennel. There was no movement as his family called his name,” Mara wrote. “I held her baby as the mother attempted to resuscitate their 10 month old puppy. I cried with them three minutes later as she sobbed over his lifeless body.”

“This poor family paid $125 for their pet to be murdered in front of them. There is no excuse for the pain this family is suffering,” Mara wrote.

I want to help this woman and her daughter. They lost their dog because of an @united flight attendant. My heart is broken. pic.twitter.com/mjXYAhxsAq — MaggieGremminger (@MaggieGrem) March 13, 2018

Another passenger tweeted a photo of the mother and her children after finding out the puppy had died during the flight. The puppy carrier is seen in the photo next to the stroller.

United Continental (UAL) apologized for the dog’s death in an emailed statement on Tuesday:

“This was a tragic accident that should never have occurred, as pets should never be placed in the overhead bin. We assume full responsibility for this tragedy and express our deepest condolences to the family and are committed to supporting them. We are thoroughly investigating what occurred to prevent this from ever happening again.”

United is still investigating the incident. The flight attendant reportedly told the airline she did not realize the dog was inside the carrier, but witnesses dispute that.

The family does not plan to fly with United again.