EDMONTON -- Alberta Health Services is apologizing and has launched an internal investigation after sending a teenage Indigenous girl a letter addressed to "Treaty Indian."

"The address line of the letter contained completely inappropriate and culturally offensive language, which should never have been used," the provincial health organization said in a statement Thursday.

"We sincerely and unreservedly apologize for any offence or concern this has caused. This should not have happened, and we are profoundly saddened that it has."

The organization said it has reached out to the 15-year-old girl and her mother to apologize personally. It is also apologizing to Indigenous communities and promised to explain how this might have happened.

"This in no way reflects the beliefs or values of AHS, and is no way indicative of our relationship with First Nations and Indigenous people," the statement said.

The health service said all employees are expected to treat everyone with respect and it will make sure something similar never happens again.

"We know that a significant barrier to First Nations people accessing the health-care system is trust, and acknowledge that institutional racism and stereotyping has kept people from getting the care they need," the health service said.

"We also know that the relationships between AHS and our First Nations people must continue to improve, and we are committed to building, nurturing and growing those relationships."

The CEO of Alberta Health Services apologized last summer when a health services official who had conducted a seminar for educators at a southern Alberta First Nation sent a text complaining she had been yelled at by "a rabid squaw." The worker who sent the text message and another who was intended to receive it were fired.

The letter came to light when a picture of the address line was posted on Twitter Wednesday by Indigenous artist Dawn Marie Marchand.

She said the letter was addressed to the daughter of a friend who gave her permission to share it on social media.

"(It's) hard to understand how it is even possible," she wrote. "It basically means someone could not even be bothered to find out the name."

Following the apology, Marchand said the girl's mother did not wish to comment on the mistake.

"To her, this is just another example of how we are dehumanized in institutional situations," Marchand wrote on Twitter.

"Although she wanted to show her disappointment, she does not want to make any statements in the media about this publicly. She is already dealing with enough."

Alberta Health Minister Sarah Hoffman said the letter was completely unacceptable.

"If I was a mother receiving a letter like that for my child I would be incredibly insulted and offended that they didn't even put the name on the letter," she said Thursday.

"I have raised this with AHS and they too are appalled and apologize. Definitely it was not intentional. They've attempted to contact the family and they've begun an investigation to find out how it did happen to ensure that it doesn't happen again."