Azerbaijan denied any connection to the arrest of Germany's former spy chief August Hanning, calling the reports "disinformation" and a "smear campaign" aimed at damaging Baku-Berlin relations.

Hanning, who led the BND from 1998 to 2005, was detained on suspicion of treason after allegedly buying classified documents and preparing an analysis for an unnamed foreign intelligence service.

Der Spiegel reported the foreign link was Azerbaijan.

Baku has lodged a formal protest with both the German Chancellor's Office and Foreign Ministry.