A 17-year-old girl — believed to be an innocent bystander — was shot in the back at a Brooklyn house party, police and sources said Wednesday.

The teenager was struck in the lower back, possibly by a stray bullet, around 10:15 p.m. Tuesday inside the home on East 70th Street near Avenue N in Bergen Beach, cops and police sources said.

She was taken to Maimonides Medical Center, where she was listed in stable condition. 

The girl was not believed to be the intended target, sources said. 

The motive for the violence remained under investigation Wednesday.

No arrests have been made.