The inquiry investigating the resignation of Martin Callinan as Garda Commissioner is to call some witnesses back for further hearings.

The Fennelly Commission says "an issue has emerged" which needs further clarification, and further oral evidence is needed.

Witnesses will now be called back in the coming days and the first draft of the report will be circulated before the end of the month.

If that's the case, the final report into the circumstances of Callinan's departure will not be expected until at least the end of June.