Two Australian women arrested upon their return to Melbourne from Syria have been charged with multiple crimes against humanity, following a long-running counter-terrorism investigation.

The women, aged 53 and 31, were taken into custody at Melbourne Airport on Wednesday after arriving in Australia, before being charged by the Victoria Joint Counter Terrorism Team (JCTT), a taskforce comprising the AFP, Victoria Police and ASIO.

They are due to face the Melbourne Magistrates Court on Friday.

The 53-year-old woman has been charged with four offences: enslavement, possessing a slave, using a slave and engaging in slave trading. Each offence carries a maximum penalty of 25 years’ imprisonment.

It will be alleged that she travelled to Syria in 2014 with her husband and children and was complicit in the purchase of a female slave for US$10,000, before knowingly keeping the woman in the family home.

The 31-year-old woman has been charged with two offences, enslavement and using a slave, which also carry maximum penalties of 25 years behind bars.

Authorities will allege she also travelled to Syria in 2014 with her family and knowingly kept a female slave in the home.

Both women had been detained by Kurdish forces since March 2019, when they were captured and held with family members in the Al Roj Internally Displaced Persons camp.

AFP Assistant Commissioner for Counter Terrorism Stephen Nutt said authorities had been preparing for the potential return of Australians from conflict zones for more than a decade.

“Australian JCTTs methodically investigated all Australians who travelled to declared conflict areas and will ensure those who are alleged to have committed a criminal offence are put before the courts,” Assistant Commissioner Nutt said.

“JCTTs include some of the most experienced national security investigators and analysts in our country.

“This remains an active investigation into very serious allegations.”

He said operational planning began in 2015 and was later formalised under a national operation known as Kurrajong.

Victoria Police Assistant Commissioner Martin O’Brien said authorities were working closely with partner agencies to ensure community safety remained the top priority.

“Victoria Police will continue to work closely with our law enforcement partners and other agencies to ensure there is no risk to our local community,” Assistant Commissioner O’Brien said.

“We want to reassure all Victorians that anyone residing in our state who has committed serious criminal offences, including those returning from conflict areas, will be held to account.”

Authorities said the investigation remains ongoing.

A third woman was also arrested after arriving in Australia, with separate charges laid in Sydney.

The 32-year-old was taken into custody at Sydney Airport on Thursday night and later charged with entering or remaining in a declared conflict area and being a member of a terrorist organisation. Both offences carry a maximum penalty of 10 years’ imprisonment.

It will be alleged she travelled to Syria in 2015 to join her husband, who had previously left Australia and joined ISIS.

She is expected to face court in Sydney on Friday.