SYDNEY (Reuters) - Australia has arrested and charged a Sri Lankan man with planning a terror attack after finding “symbolic locations within Sydney” listed as possible targets in his notebook, police said on Friday.

A staunch U.S. ally, Australia has been on heightened alert from 2015 for attacks by home-grown militants returning from fighting in the Middle East, and its intelligence agencies have stepped up scrutiny.

The 25-year-old was arrested on Thursday in Sydney, charged with preparing a terror offense and is in custody while his home and workplace at a university are searched, New South Wales police official Mick Sheehy told reporters.

“From the documentation, he would affiliate with ISIS,” Sheehy added, using an acronym for militant group Islamic State.

“There is a number of locations and individuals named in that document who are potential targets,” Sheehy, a detective acting superintendent, said of the notebook, adding that it needed further analysis.

The man did not have the “capability” to launch an attack, however, he said, and ruled out any threat to the public.

Reuters was not immediately able to trace contacts for the man’s lawyer, or other representatives, to seek comment.

Authorities say Australia’s vigilance has helped to foil at least a dozen plots, including plans to attack downtown Melbourne at Christmas in 2016 and a plot to blow up a flight from Sydney to Abu Dhabi.

In Dec. 2014, two hostages were killed during a 17-hour siege by a “lone wolf” gunman, inspired by Islamic State militants, in a cafe in Sydney.