DÜSSELDORF, Germany—Top federal and regional security officials met seven times to discuss the potential danger posed by Tunisian migrant Anis Amri in the year before he attacked a Berlin Christmas market, the latest revelation in a string of mishaps that failed to prevent the attack.

The new details, disclosed by security officials at a regional parliamentary hearing Thursday, suggest that German security and intelligence authorities miscalculated the immediate threat that Amri presented. Despite extensive surveillance, efforts...