OSLO, Norway — The Norwegian police have concluded that footage showing the brutal killing of a Scandinavian tourist in Morocco by suspects who also filmed themselves pledging allegiance to the Islamic State is most likely authentic.

Norway’s National Criminal Investigation Service, known as Kripos, said in a statement on Friday, “There is no concrete evidence indicating the video is not real.”

It came as the Moroccan authorities announced the arrests of nine more people in connection with the killing of the university students Maren Ueland, 28, of Norway and Louisa Vesterager Jespersen, 24, of Denmark, in a remote corner of the Atlas Mountains. Morocco considers the killings a terrorist act.

Thirteen men in all have been detained in the case. Morocco’s Central Bureau of Judicial Investigations said the nine new suspects had been arrested in the regions of Marrakesh, Essaouira, Sidi Bennour, Tangier and Chtouka Ait Baha. They were carrying arms and “suspicious materials” used in the manufacture of explosives at the time of their arrests. No further details were released.