Investigators say the deadly Bondi Beach attack is being treated as ‘terrorism’ after evidence of ISIL influence found.

The Australian police say the two men accused of carrying out a deadly shooting at a Jewish Hanukkah celebration at Sydney’s Bondi Beach that killed 15 people were “inspired” by the ISIL (ISIS) group.

Police also confirmed on Tuesday that they were investigating a trip the two suspects undertook to the Philippines last month.

“Early indications point to a terrorist attack inspired by Islamic State, allegedly committed by a father and son,” Australian Federal Police Commissioner Krissy Barrett said at a news conference.

“These are the alleged actions of those who have aligned themselves with a terrorist organisation, not a religion,” Barrett said, referring to ISIL.

One of the alleged attackers, identified by police as 50-year-old Sajid Akram, was shot dead by police officers. His 24-year-old son, believed to have acted alongside him and named by local media as Naveed Akram, was also shot and remains in critical condition in hospital.

Investigators say the father-son duo opened fire on hundreds of people gathered at the beachside festival, carrying out the attack that lasted about 10 minutes at one of Australia’s most popular tourist locations.

Wayne Hay, reporting for Al Jazeera from Bondi Beach, said police confirmed that “two Islamic State flags – homemade flags – were found in the gunmen’s vehicle along with an improvised explosive device”.

“They also spoke about this trip that the pair had taken to the Philippines. A lot of speculation about that over the past 24 hours or so. They confirmed that they did go to the Philippines recently, but they are not clear yet as to the motive for that trip,” Hay said.

“That will, of course, form part of any ongoing investigation as to why they made that trip,” he said.

New South Wales Police Commissioner Mal Lanyon told reporters that the reason for the visit and where they visited in the Philippines “is under investigation at the moment”.

The Philippine police said they are also investigating the matter.

ISIL-linked armed groups are known to operate in parts of the Philippines, particularly in the country’s south. While those groups have been significantly weakened in recent years, they continue to exist as smaller cells on the southern island of Mindanao.

Their strength is far removed from the influence they once exerted, particularly during the 2017 siege of Marawi, when ISIL fighters laid siege to the city, prompting months of heavy combat with government forces that killed more than 1,000 people.

The Bondi Beach attack, which was the deadliest mass shooting in Australia in almost three decades, also left some 25 people injured, including several in critical condition.