FRANKFURT: The European Central Bank said on Friday it had found capital shortfalls at two out of six Bulgarian banks that it would now help supervise, a preliminary step in Sofia's efforts to join the euro zone.

First Investment Bank was found to have a capital shortfall of 262.9 million euros ($292.42 million) while Investbank came up short by 51.8 million euros, the ECB said after conducting a health check of the six banks.

UniCredit Bulbank, DSK Bank, United Bulgarian Bank and Central Cooperative Bank all passed the test.

The ECB's asset quality review and stress tests are part of Sofia's efforts to join the banking union and the "waiting room" for euro zone membership this year.