A royal commission investigating Australia's deadliest mass shooting in 30 years has revealed that a Jewish community group warned police of a "likely" terror attack just days before the December assault on Bondi Beach.

Sajid Akram and his son Naveed are accused of opening fire as Jewish families gathered for a Hanukkah celebration, killing 15 people. The inquiry confirmed the Jewish community was the "evident target."

The Community Security Group had emailed police stating, "A terrorist attack against the NSW Jewish Community is likely," but was told dedicated officers could not be provided for the festival-only mobile patrols.

New South Wales Premier Chris Minns accepted responsibility, saying, "If we had known what was going to happen, we would have put an army down there."

The inquiry also noted that Australia's counter-terrorism capabilities "could be improved" and urged the government to prioritize a stalled gun buyback scheme.

Sajid Akram was killed by police. His son Naveed, an Australian-born citizen, remains in custody, charged with terrorism and 15 counts of murder.