FRANKFURT (Reuters) - The European Central Bank has asked for clarification from Deutsche Bank about a 28 billion euro (£24 billion) mistaken transfer that the German lender made in March, a German newspaper reported on Friday.

Deutsche Bank earlier on Friday said it had made the transfer in error to its own account at the derivative exchange Eurex, confirming news first reported by Bloomberg.

The bank said it noticed the mistake in a matter of minutes and there was no financial damage.

The ECB, which oversees Deutsche Bank, has sent a questionnaire to the bank about the incident, Handelsblatt reported. Questions include why the bank's internal security controls didn't work and why there weren't two sets of eyes for the transaction.

The ECB also wants to know how Deutsche plans to prevent such an incident from happening again, the newspaper said.

The ECB declined to comment.

(Reporting by Tom Sims and Andreas Framke; Editing by Mark Potter)