Five men, with links to North African Al-Qaeda, have been arrested by security agencies over the kidnapping of a German engineer, Edgar Raupach.
The five men included a Mauritanian, sources said on Tuesday.
Four of the suspects were reportedly arrested during a raid on a store owned by the Mauritanian in Kano last week.
Thje fifth suspect was arrested in a separate raid.
Raupauch was kidnapped on the outskirts of Kano.
Guns and a laptop were reportedly recovered during the raid on the store in Kano.
The North African Al-Qaeda said it was holding Raupauch, and would only release him in exchange for a jailed Muslim woman, according to a report published a few weeks ago.