CANBERRA -- The head of the Australian Defence Force (ADF) has declined to give details about how many soldiers could face criminal prosecution over alleged war crimes in Afghanistan, but warned of "uncomfortable days".

In a speech to a think tank the Lowy Institute on Tuesday, Chief of the Defence Force Angus Campbell said that the investigations continue, and the ADF needed to confront its failures.

In 2020, Campbell released a four-year inquiry by Court of Appeal Justice Paul Brereton. Credible evidence was found that soldiers from the Australian special forces committed up to 39 murders while serving in the Asian country. Altogether 19 soldiers were referred for criminal investigation.

The Office of the Special Investigator (OSI), established in the wake of the report, has said it is investigating more than 40 alleged offenses.

"The OSI, which is working independently, has seen a first arrest and charging of a former soldier," he said, according to the Australian Broadcasting Corporation.

"You won't see me trying to gloss over these things, and I think that there could be some very uncomfortable days coming forward," Campbell said.