Sydney, Australia - A father and son who killed 15 people attending a Jewish festival on Sydney's Bondi Beach had possible links to the Islamic State group, the Australian Broadcasting Corporation said Monday.

Police have yet to provide a motive for Sunday's mass shooting, but they say it was clearly an antisemitic, terrorist act.

Senior officials in the investigation told the ABC that two IS flags were found in the gunmen's car at the beach, although New South Wales police said they could not confirm the report.

Details of the pair are emerging in the hours since the black-clad, 50-year-old father and his 24-year-old son were seen side-by-side on a small bridge, firing long-barreled guns at people on the beach.

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The father, named in local media as Sajid Akram, was killed in a shootout with police, detectives say.

He had licenses for six guns, and police say they believe all of them were used to kill and wound people enjoying a sun-splashed day at Australia's best-known beach.

The father first came to Australia in 1998 on a student visa, Home Affairs Minister Tony Burke told reporters on Monday.

In 2001, he obtained a visa granted to the partners of Australian citizens or permanent residents.

Since then, the government says he traveled overseas three times.

His son – an Australian-born citizen according to the home affairs minister – is critically injured in a Sydney hospital bed under police guard.

Prime Minister Anthony Albanese confirmed Monday that the son – named in local media as Naveed Akram – came to the attention of Australia's security services in 2019.

"He was examined on the basis of being associated with others, and the assessment was made that there was no indication of any ongoing threat or threat of him engaging in violence," Albanese said.

Australia's public broadcaster ABC said Naveed Akram was believed to be closely connected to an Islamic State member who was arrested in July 2019 and convicted of preparing a terrorist act in Australia.

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The broadcaster said counter-terrorism detectives believed the two Bondi Beach gunmen had pledged allegiance to Islamic State.

Police said they raided two properties in western Sydney during their investigations.

One was in the suburb of Bonnyrigg where local media said Naveed Akram lived, and the other was a home in Campsie where the father and son reportedly stayed before carrying out their attack.

The Australian Security Intelligence Organisation said it "does not comment on individuals or ongoing investigations."

"We want to understand the motive behind these two people," New South Wales police commissioner Mal Lanyon told reporters.

"We want to understand whether these people were further involved in any offences, but we have no history to say that's the case."