The ECB is the supervisor for top banks in the single currency area.

The European Banking Authority (EBA), the EU's banking watchdog which designs and coordinates the pan-European stress test, has said the exercise will start in the first quarter.

"We will use the criteria of EBA to define the size of the exercise," Danièle Nouy, chair of the ECB's banking supervisory arm, said in an interview with Finnish broadcaster YLE aired on Thursday.

"My view would be about 50-60 banks, the most relevant for such a stress test."

The ECB spokeswoman confirmed the figures.

The ECB tested 130 euro zone banks in 2014, in a broader exercise aimed at improving confidence in the sector before the Frankfurt-based central bank became a supervisor last November.

(Reporting By Francesco Canepa and Huw Jones; Editing by Keith Weir)