German conservative leader Friedrich Merz has demanded fundamental changes to migration policy and a dramatic increase in deportations after the deadly stabbing in the southern city of Aschaffenburg.

The conservative leader wants to impose strict border controls after knife killings in Aschaffenburg this week.

Germany's main opposition leader vowed on Thursday to impose immediate border controls if he becomes chancellor, as expected, after elections next month, a day after an Afghan asylum seeker was arrested for a deadly knife attack targeting children.