Australian soldiers who flew a Nazi swastika flag over their fighting vehicle in Afghanistan more than a decade ago were ‘wrong’ and punished at the time, Australia's prime minister said on Thursday, after a picture of the incident emerged.

The flag was attached to a military jeep in the photo taken during a patrol in Afghanistan in 2007, according to the Australian Broadcasting Corporation (ABC), which published the picture.

‘The flag obviously was removed and the personnel involved were disciplined,’ Prime Minister Malcolm Turnbull told reporters in the Tasmanian state capital of Hobart, without specifying their punishment.

‘It was absolutely wrong and their commanders took action at the time,’ he said.

Australia, a staunch US ally, has had troops in Afghanistan for 17 years fighting against the Taliban and other militants.

Their behaviour between 2005 and 2016, including accusations that they used illegal force and showed a disregard for human life during missions, is being investigated by defence authorities.

The swastika in the photo was the emblem of Germany's Nazi Party.

‘It is completely unacceptable to use a flag of this nature,’ Australia's defence minister, Marise Payne, said in an emailed statement.

‘This is completely at odds with the values of the Australian Defence Force (ADF) and the tens of thousands of ADF personnel who have served with distinction in Afghanistan.’

In recent days the Sydney Morning Herald newspaper has published stories, citing unidentified witnesses, alleging Australian troops mistreated and executed prisoners in 2009 and 2012. The ABC has previously reported on an alleged cover-up of the killing of an Afghan boy by Australian special forces.

Australia's defence department did not immediately respond to a request for comment on the news reports, but it has previously said it is ‘aware of allegations of significant issues’ during Afghanistan deployments and that they are being investigated.