Five Australian teenagers were arrested in Melbourne on Saturday for allegedly planning an ISIS-inspired attack at an event honoring veterans from World War I, the Associated Press reported.

The teens, ages 18 and 19, are accused of plotting an attack that included targeting police officers at the ANZAC Day ceremony on April 25 in Melbourne, Australian Federal Police Acting Deputy Commissioner Neil Gaughan said.

Two 18-year-olds were arrested for planning the assault. Another 18-year-old was picked up on a weapons charge. The last two suspects, ages 18 and 19, were said to be in custody and cooperating with police, the AP reported.

The arrests come after months of surveilling the teenagers, who had ties to alleged ISIS supporter 18-year-old Numan Haider, who was shot and killed after he stabbed two Melbourne cops last September, police said. 

Police said the attack would have involved "edged weapons" and was inspired by the Islamic State of Iraq and Syria, which is known for beheading hostages and releasing videos of the heinous acts. 

"At this stage, we have no information that it was a planned beheading. But there was reference to an attack on police," Gaughan said, according to the AP. "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."

Michael Phelan, federal police deputy commissioner, said authorities took immediate action when they caught wind of a specific attack, the AP reported.

"This is a new paradigm for police," Phelan said. "These types of attacks that are planned are very rudimentary and simple. ... All you need these days is a knife, a flag and a camera and one can commit a terrorist act."

Australia raised its terror threat level when the Islamic State in September encouraged its supporters located in other countries to carry out attacks, including Australia. Two months later, a self-proclaimed ISIS supporter launched a siege at a chocolate cafe in Sydney that ended with his death and the deaths of two hostages.

After Saturday's arrests, Australian Prime Minister Tony Abbott encouraged people to attend the ANZAC Day event, held annually to mark the first major battle fought by the Australian and New Zealand Army Corps in 1925.

"The best sign of defiance we can give to those who would do us harm is to go about a normal, peaceful, free and fair Australian life," Abbott said.