The mother-in-law of one of Australia's most notorious Daesh fighters has pleaded for the government to help her "desperate" daughter and five grandchildren flee the Middle East, saying she made "the mistake of a lifetime".

Karen Nettleton's emotional appeal for help came after reports that her son-in-law Khaled Sharrouf and his friend Mohamed Elomar were killed in fighting in the Iraqi city of Mosul in the past week, although officials Wednesday suggested they may have died in Syria.

Sharrouf gained global infamy last year when he posted pictures on his Twitter account showing himself and his seven-year-old, Sydney-raised son holding up the severed heads of slain soldiers in Syria.

One of his other children married Elomar, who was also pictured with severed heads, when she was aged just 13. They all left for Syria in 2013.

"With the deaths of Mohamed Elomar and likely Khaled Sharrouf, my daughter and grandchildren more than ever need the love and care of their family to help them recover from the trauma, abuse and terrors of war they have experienced," Nettleton said in a statement late Tuesday.

"Unlike millions of displaced people in Iraq and Syria, they have a place to come home to."

She added that "my daughter made the mistake of a lifetime".

"Today she is a parent alone in a foreign and vicious land looking after a widowed 14-year-old and four other young children."

She implored Prime Minister Tony Abbott to help bring them home.

"Mr Abbott, I beg you, please help bring my child and grandchildren home."

While the deaths of the two men have not been confirmed, Canberra on Wednesday said there "is a high level of certainty in relation to Elomar" but that there was "less certainty in relation to Sharrouf".

Abbott, whose government on Wednesday introduced new laws into to parliament to strip dual nationals linked to terrorism of their citizenship, said he felt for the children.

But he also warned that if Nettleton, who converted to Islam and married Sharrouf 10 years ago, returned home she would face "significant consequences", while not offering any help for her to do so.

"You can't convict the kids on the basis of the crimes of the parents but nevertheless, they will be dealt with in exactly the same way as the families of criminals are normally dealt with," he said.

"These aren't the first Australians who have committed very serious crimes overseas, who have families. They will be dealt with in the normal way."

Foreign Minister Julie Bishop said no decision would be made on whether Sharrouf's wife and children would be helped to return until they have confirmed his death.

Abbott said Tuesday about 120 Australians were fighting in Iraq and Syria, with some 30 believed to have been killed. The government said last month another 30 had returned from the region.
Source: AFP