FRANKFURT, May 16 (Reuters) - The European Central Bank has stopped monetary policy operations with some Greek banks as they have not been successfully recapitalised, euro zone central bank sources said on Wednesday.

The ECB declined to comment.

The ECB only conducts its refinancing operations with solvent banks. With no access to ECB funds, the banks concerned must go to the Bank of Greece for emergency liquidity assistance (ELA).

It was unclear exactly how many banks were affected.

One person familiar with the matter said four Greek banks' capital was so depleted they were operating with negative equity capital. According to its own rules, the ECB cannot provide liquidity to banks in such a situation.

The ECB said earlier on Wednesday it continued to support Greek banks. (Reporting by Annika Breidthardt and Andreas Framke; Writing by Paul Carrel; Editing by Noah Barkin)