The older sister of a radicalised teen gunman who killed NSW Police accountant Curtis Cheng has herself been killed after joining Islamic State in Syria.
Shadi Jabar Khalil Mohammad died in a US air strike on the Syrian city of Al Bab on April 22 alongside her husband Abu Saad al-Sudani, according to the United States government.
Defence Minister Marise Payne described the couple as "both active recruiters of foreign fighters on behalf of ISIL, and had been inspiring attacks against Western interests".
Shadi Jabar, a 27-year-old student, is the sister of 15-year-old Farhad Jabar, who was shot and killed by police after fatally shooting Mr Cheng outside Parramatta police headquarters on October 2 last year.
A day earlier, Shadi Jabar boarded a flight to Singapore, then Turkey, believed to be intended for Syria or Iraq.
Her family told police at the time that she had taken all her belongings from the North Parramatta home she shared with them.
Another sibling, 22-year-old Farshad Jabar, is believed to have gone to Iraq just days after his teen brother's funeral in October.
The family moved to Australia from Kurdistan 15 years ago, but it's believed Farshad Jabar wanted to return overseas to escape media attention.
NSW Premier Mike Baird said he had not spoken to Mr Cheng's family about the reports, and said it was difficult to know if the reports were true.
"Clearly our thoughts are with the (Cheng) family because that is a case that brings back obviously significant memories and is painful and difficult for them to deal with," he told reporters on Thursday.
Shadi Jabar's husband, Abu Saad al Sudani, has been described as a "media expert" for Islamic State who helped to fund a terror cell through electronic funds transfer.
In posts online the man known as the Beast of Islam called for donations to help fund items including drones, night vision, sniper scopes, "daily expenses for mujahdeen and any beneficial items for mujahdeen".
Last week Sydney man Milad Atai, 20, faced Goulburn Local Court accused of being a member of Islamic State and of helping Shadi Jabar flee to Syria.
"These incidents remind us that Australians who engage in terrorist activity and move into overseas conflict zones are placing themselves and others at significant risk," Ms Payne said.
