A woman was in custody Saturday night after a man was fatally stabbed in a St. Paul apartment complex, police said.

Officer responded to a report of an injured man in the 1100 block of Hamline Avenue N. around 1 p.m. The man, who has yet to be identified, was taken to Regions Hospital, where he died of a single stab wound to the upper body, according to police spokesman Steve Linders.

The woman, who was in the apartment when officers arrived, was arrested. Police are not sure what the relationship was between the two.

The Ramsey County medical examiner will identify the victim and determine the cause and manner of death.