(CNN) Two of Australia's most infamous terrorists who left Australia to fight for ISIS have been killed, a close relative said.

Khaled Sharrouf and Mohamed Elomar died in a drone strike in ISIS-controlled territory, said Zaynab Sharrouf, 14. The teen is Khaled Sharrouf's daughter and Elomar's wife, having married 31-year-old Elomar, her father's best friend, in March.

The men were getting into a car when they were struck, she told CNN. Australian media reported that the men were in the ISIS stronghold of Mosul, Iraq.

Australian authorities are working to confirm their deaths independently.

Prime Minister Tony Abbott told CNN affiliate Channel 7 Wednesday there was a "high degree of confidence" that Elomar had been killed, but with regard to Sharrouf, "we can't say."

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Sharrouf gained infamy last year when he tweeted a picture of his 7-year-old son holding a severed head. The image was captioned, "That's my boy."

At the time, U.S. Secretary of State John Kerry called the picture "one of the most disturbing, stomach-turning, grotesque photographs ever displayed."

Sharrouf and Elomar also tweeted pictures of themselves with the decapitated heads of Syrian government fighters, prompting Australian Federal Police to issue arrest warrants for the pair in July.

Passports canceled

The pair had had their Australian passports canceled on the grounds that they posed a security risk to Australia, Foreign Minister Julie Bishop said.

"They are criminal thugs who have been carrying out brutal terrorist attacks, putting people's lives in danger," she told reporters Tuesday.

"They boast of the brutality and violence they have been meting out to people, they boast of having sexual slaves."

Elomar had claimed online to have sold captured girls as slaves for $2,500 each, and in August he triggered security concerns for an Australian Muslim leader after offering a $1,000 bounty for information on the man's whereabouts

Sharrouf, who in 2009 was jailed for his role in a planned terror attack in Australia, traveled to Syria with his wife, Tara Nettleton, and their family in 2013, using his brother's passport to slip past authorities.

Let family return?

The Australian government now faces the question of whether to allow Sharrouf's wife and children to come home.

Khaled Sharrouf's daughter, 14, posted this photo of women in her family online, the Institute of Strategic Dialogue says.

Tara Nettleton's mother, Karen Nettleton, issued a plea to Australian PM Tony Abbott Tuesday to allow her daughter and grandchildren to return following the two men's deaths, Australia's Daily Telegraph newspaper reported.

"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 said.

"I accept that some will be critical of my daughter, who followed her heart and has paid an enormous price. Mr Abbott, I beg you, please help bring my child and grandchildren home."

'A good day'

Nettleton's father, Peter Nettleton, welcomed the news of Sharrouf and Elomar's deaths, the newspaper reported.

"It's a good day isn't it? I was ecstatic when I heard (Sharrouf) was dead," he said.

Bishop said no decision would be made on whether the family could return until the deaths of Sharrouf and Elomar were verified.

"These are details we will consider once the reports have been verified one way or another," she said Tuesday.

Abbott told Channel 7 Wednesday Sharrouf's children would be treated like the families of other criminals.

"Yes, 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."

In May, Australian media reported that Nettleton was seeking to return home from Syria with the couple's children, where it was believed they had been living in the ISIS stronghold of Raqqa.

At the time, Abbott said Nettleton would face the "full severity" of the law if she dared to return.

"I'm afraid you don't get off scot-free just because you say, 'I've seen the error of my ways,' " he said. "If you commit serious crimes, you should face serious punishment, and as far as I'm concerned, that will always be the case."

Sharrouf's teen years

Born in Australia in February 1981, Sharrouf was the son of Lebanese parents who had a violent relationship with his father and spent most of his youth in and out of local courts. Details of Sharrouf's troubled teenage years were revealed in court documents from his sentencing in the New South Wales Supreme Court in 2009 on terror-related charges.

According to the documents, Sharrouf was expelled from school for violent conduct and "was soon drawn into bad company."

He appeared before the courts on a number of minor charges between 1995 and 1998 when he was also regularly taking amphetamines, LSD and ecstasy. The drugs were likely to have been a "significant factor" in the emergence of schizophrenia, the documents said.

Role in attack plot

Sharrouf was a laborer in the building industry for a time but survived mostly on a disability support pension until his November 2005 arrest on terror-related charges.

He was one of nine detained after a series of raids on homes and businesses as part of an investigation into a plot for a terror attack in Australia by Islamic extremists. The plot was led by Elomar's uncle Mohamed Ali Elomar, currently serving a minimum 21-year sentence.

Sharrouf pleaded guilty to possessing batteries and clocks, knowing they were to be used to make explosives for a terrorist act. However, Sharrouf's hearing was delayed after he was found to be unfit to stand trial due to mental illness.

In November 2007, a court-appointed specialist said he was suffering an "acute exacerbation of the illness schizophrenia." He was put on medication, and in early 2009, it was deemed he had made a "remarkable recovery."

Sharrouf was sentenced to five years and three months in prison. He had already served most of that time while awaiting trial and was released from prison after three weeks.