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.

Friedrich Merz, the conservative front-runner in the race for Germany’s chancellorship, called for a radical overhaul of the country’s migration policy including permanent border checks. The comments come after an asylum seeker from Afghanistan was taken into custody over a fatal stabbing of a two-year-old child and a man in a park on Wednesday.