The prosecution against Melbourne man Jamie Reece Williams, charged in 2015 with attempting to travel to northern Iraq to fight with Kurdish forces against Islamic State (IS) militants, has been dropped.

The decision to discontinue the prosecution was made by Federal Attorney-General George Brandis.

The move could have ramifications for Australians who have fought against IS, returned to Australia, but are still under investigation by the Australian Federal Police.

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Mr Williams, of Epping, in Melbourne’s northern suburbs, was charged in July last year after being detained at Melbourne Airport in 2014 as he attempted to board a flight to the Middle East.

When asked what he was travelling for Mr Williams told authorities he was going to fight with a Kurdish militia called the YPG, and planned to travel first to the northern Iraqi city of Sulaymaniyah.

Late last year Mr Williams’ lawyers applied to have the case against their client discontinued by the Commonwealth Director of Public Prosecutions (CDPP), arguing that the prosecution was not in the public interest because the Kurds are an ally of the coalition fighting against IS.

They also said the YPG was in fact the effective government of parts of northern Syria.

Under the foreign fighters legislation, which Mr Williams was charged under, anyone who fought with or planned to fight with the armed forces of a government was exempt from prosecution.

Mr Williams’ lawyers argued that the YPG and its political wing exerted “effective control” over parts of Syria, and therefore constituted a government under the act.

It is not clear on what grounds the CDPP has decided to discontinue the prosecution.

– ABC