The 29-year-old, identified as Sief Allah H., was detained after police stormed his flat in Cologne late on Tuesday.
Germany's interior minister outlined plans for an overhaul of the country's security apparatus, seeking greater federal powers on domestic intelligence and the enforcement of migrant expulsions in the wake of the Berlin truck attack.
Fingerprints from a Tunisian migrant have been found inside the truck that smashed through a Berlin Christmas market on Monday in an attack that killed 12 people, German Interior Minister Thomas de Maiziere said.
German police launched a manhunt Wednesday for a rejected asylum seeker suspected of involvement in a deadly truck assault on a Berlin Christmas market claimed by the Islamic State jihadist group.
Tunisia is eyeing to raise a $2bn joint-investment fund with Qatar to be invested in a range of sectors, including food production and manufacturing, an official of the Tunisian Confederation of Industry, Trade, and Handicrafts has said.
Algerian troops killed a jihadist east of the capital, the defence ministry said, bringing to 12 the number of gunmen killed by security forces in a week.
French investigators have found no evidence that a man who drove his car into troops guarding a mosque in southern France on New Year's Day was linked to a terrorist group, a local prosecutor said.