Australian-born Jake Bilardi, who became known as "Jihadi Jake", has died in a suicide bomb attack, reports say.
Islamic State propaganda suggested the 18-year-old was part of a coordinated suicide attack involving Russian, Australian, Moroccan, Egyptian, Uzbek, Syrian and Belgian fighters in the Iraqi city of Ramadi on Wednesday.
At least 10 people were killed and 30 wounded when 13 car bombs detonated in Anbar province.
Bilardi, who was identified as prominent IS tweeter Abu Abdullah al-Australi on Tuesday, dropped out of his Australian school last year and bought a one-way ticket to Turkey before making his way to Syria.
Australian Foreign Minister Julie Bishop said: "I can confirm that we're seeking to independently verify that he was part of this suicide bombing attack.
"The news appears very grim, but we are seeking to independently verify it."
According to the Islamic State propaganda, Bilardi drove a white van packed with explosives into a target in Ramadi. A picture of him behind the wheel was tweeted by IS militants with the caption "May Allah accept him".
Hikmat Suleiman, the political adviser to the governor of Anbar, said Iraqi forces were able to thwart the majority of the attacks by destroying or detonating the car bombs before they reached their targets.
Also known as the "white jihadi", Bilardi converted to Islam at the age of 13 following the death of his mother.
The famous picture of Bilardi clutching a rifle and flanked by two militants was shared on social media in December, alleging that he was actually a British teenager.
Scotland Yard pointed out that no missing persons had been reported under that name and the UCAS deadline had not yet passed. The teenager in the picture was later identified as Bilardi by friends in Melbourne and members of his mosque.
"He used to come here when we had a big lecture," said Abu Zaid, a committee member of the Hume Islamic Youth Centre in Coolaroo.
"He was a very quiet guy, he stuck to himself. We weren't close to him. I didn't see any of the people [getting] close to him."
In December Bilardi told the BBC of his desire to become a martyr, saying: "I've been waiting for almost one month now and I'm next to go so inshallah [God willing] it'll be soon. I came here chasing death, I might as well kill as many kuffar (infidels) as I can."
Australian Prime Minister Tony Abbott said: "It's very, very important that we do everything we can to try to safeguard our young people against the lure of this shocking, alien and extreme ideology."
A blog, thought to be written by Bilardi, documents his journey of radicalisation and reportedly claimed he had plans to bomb Melbourne before fleeing to join the Islamic State.