The victim was stabbed in the chest in an apartment in the city’s Grim district. She was taken to Sørlandet hospital where she died from the injuries sustained in the attack.
Police said they were unsure if the suspected attacker was Iraqi or Iranian since he operated with two separate identities.
Chief investigator Geir Hansen said the suspect had received permission to remain in the country while he appeals a deportation order issued last year by the Norwegian Directorate of Immigration.
The Eritrean victim had received a permanent residency permit last year.
Police confirmed that the alleged attacker and his victim were both registered as living at the address where the stabbing took place.
“To the best of my knowledge there were no witnesses to the incident itself,” said investigator Hansen.
Police said they could not yet establish a motive for the attack.
A remand hearing has been scheduled for Thursday, newspaper Fædrelandsvennen reports.
Police could not say whether it was the attacker or somebody else who alerted them to the attack at 1.46am on Wednesday. The victim was pronounced dead at 2am.