The story was given front-page treatment in several newspapers, but the coverage contained unsubstantiated opinions as well as reports about the incident in which a self-styled cleric and two hostages died.
"Daesh reached Australia," said Khorasan, a conservative daily, using the Arabic acronym for the IS group. The headline in Mardom Salari, a reformist title, read: "Daesh suspect killed by police."
Australian officials have said the gunman, Man Haron Monis, who had been in the country for almost two decades, "had a long history of violent crime, infatuation with extremism and mental instability".
Monis converted from Shiism, Iran's official religion, to Sunni Islam, according to a post on his website.
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In its only official comment on the deadly siege, Iran's government yesterday strongly condemned the 50-year-old gunman's actions.
"Undertaking such inhuman acts and provoking fear and panic in the name of merciful Islam is not in any way justifiable," foreign ministry spokeswoman Marzieh Afkham said.
However, Siasat-e-Rooz, a hardline conservative outlet, said today that "Australia's cooperation with the United States and Britain in warmongering had paved the way" for such an incident.
"The Zionist record shows that when they are faced with a global trial, they create a security crisis," said its report.
Vatan-e-Emrooz, another hardline newspaper, said Western intelligence agencies were culpable, and linked the siege to the ongoing battles against IS in Iraq and Syria.
"One of the main gaffes of Australia's security service, which is under the influence of the CIA and MI6, was to provide the Daesh black flag for this terrorist, as he mistakenly had carried the Saudi Arabia flag and put it up in front of the cameras," the newspaper said.