Located where the Berlin Wall once dissected the city, the huge 1.1-billion-euro ($1.25-billion) complex now houses 4,000 of the spy agency's 6,500 staff.

Built on the former site of an East German sports stadium, it is one of the world's largest secret service bases, covering 10 hectares – the equivalent to 36 football fields.

Pointing to a host of global threats from terrorism to cyber-attacks, Merkel thanked the BND staff for their work "so that millions of Germans can live in safety."

For the BND, which until now has been cloistered away in a former Nazi settlement outside Munich since its founding after World War II, its bold new presence is meant to signal a more self-confident global role.