Seven people were arrested near Bondi Beach on Thursday over what authorities believe was a second planned terrorist attack, just days after Islamic State group-affiliated gunmen massacred over a dozen Hanukkah celebrants.

The two gunmen behind Australia’s worst mass shooting in nearly three decades appeared to have acted alone and were likely inspired by Islamic State ideology, said authorities.

Fifteen people were killed and dozens wounded on Sunday in Bondi after two gunmen opened fire at people celebrating Hanukkah, the Jewish festival of lights.