An inquiry into people-smugglers serving sentences in Australian prisons has revealed that at least three of them may have been children when they were apprehended.

Under pressure from rights groups, Nicola Roxon, Australia's federal attorney-general, ordered a review into 28 cases of people who might have legally been children at the time of their convictions.

Roxon announced on Thursday that a review of the first three cases confirmed that there was sufficient reason to believe the prisoners were underage and that they should be returned to their country of origin.

"Minors don't belong in adult jails, which is why the government committed to review these cases as quickly as possible," Ms Roxon said, in comments reported by the Australian newspaper.

There are more than 200 individuals currently serving prison sentences in Australian prisons for having been members of boat crews that attempted to smuggle clandestine migrants into the country.

Most of the human traffickers are from neighbouring Indonesia.

'Embarrassing for government'

Al Jazeera's Andrew Thomas, reporting from Sydney, said: "This is embarrassing for the Australian government."

"They've made much fanfare out of going after the people-smugglers who bring desperate asylum-seekers to Australia every year."

Most of those accused of crewing the smuggling boats are convicted on aggravated people-smuggling charges.

Under Australian law, this equates to a mandatory minimum sentence of five years' imprisonment, with a three-year non-parole period.

Aside from the smugglers, there are about 3,000 asylum-seekers who have arrived in Australia in the first four months of 2012.

All asylum-seekers are put into mandatory detention while their cases are reviewed.

Many of them are also children, and there is a campaign by human rights groups to have underage asylum-seekers released.

Source: Al Jazeera and agencies