Controversial trading in eurozone government bonds by Citigroup has highlighted “systemic risks” in some smaller European countries and strengthened the case for retaining national regulators, Germany's Bundesbank has warned.

Edgar Meister, Bundesbank director responsible for financial supervision, also added to widespread calls for Citigroup's sale of €12bn ($15.3bn, £8.2bn) in bonds last August in the span of several seconds to be “investigated completely”.