United Airlines Responds to Woman Who Claims She Was Trapped Next to Masturbator

United Airlines is responding to a woman who claims she was trapped next to a man while he masturbated on a flight ... and they say they're taking her claims seriously.

The commercial air carrier tells TMZ ... "The safety of our customers and colleagues is our top priority. We take these matters seriously and are looking into what happened."

United adds ... "We have been in contact with the customer and apologized for her experience."

Remember ... the woman said she was seated next to a man on a flight from Rochester, New York, to Newark, New Jersey on Labor Day Weekend when he started pleasuring himself while looking at her.

The woman said she told flight attendants and was allowed to leave her seat until landing so she wouldn't have to sit next to the creep. The flight was full, so she had to stand.

Sources tell TMZ ... the woman spent the flight in the aircraft galley until it was time to land.

We're told the flight was operated by United's partner, Republic Airways, and United Airlines staff members didn't learn about the alleged incident until passengers were deplaning.

The woman was incensed the alleged masturbator was allowed to walk off the plane and go about his day as if nothing happened.