The European Central Bank will bring in a major auditing firm to investigate an outage that hit its payment system last month and caused delays in some payments and financial trades, ECB President Christine Lagarde said on Thursday.

The firm will look into why it took central bank staff so long to identify the problem and why back-up systems did not immediately kick in, Lagarde told European lawmakers during a hearing.

(Reporting by Francesco Canepa, Editing by Louise Heavens)