Five teenagers in the Australian city of Melbourne have been arrested on suspicion of planning an Islamic State-inspired terrorist attack, to coincide with the centenary of the landings at Gallipoli during World War One.

Two hundred police were involved in months of surveillance of the gang, but police swooped on Saturday morning when they learned an attack was imminent. It is believed they were planning to target police, and senior officials said that they found “edged weapons” including a sword and knife during the raids, the Telegraph reports.

“The act that we believe was in preparation involved attacks against police officers on Anzac Day,” said Tony Abbott, the Australian prime minister. April 25 will see a series of commemorations across Australia to mark the Australian and New Zealand entry into the war.

Neil Gaughan, the counter terrorism chief for Australian federal police, confirmed they supported the Islamic State.

“At this stage, we have no information that it was a planned beheading,” he said. “But there was reference to an attack on police. Some evidence that we have collected at a couple of the scenes, and some other information we have, leads us to believe that this particular matter was ISIS-inspired.”

All five, aged 18 and 19, were said to have links to Numan Haider, an 18-year-old who stabbed two Melbourne police officers and was subsequently shot dead in September. Haider had caught authorities’ attention months earlier over what police considered troubling behaviour, including waving what appeared to be an Islamic State group flag at a shopping mall.

The arrests emphasise Australia’s growing jihadist problem – despite its huge geographic distance from the battlefields of Syria and Iraq.