Australian counter-terror officers arrested a 40-year-old man at Sydney Airport, after he disembarked from a flight from London, and charged him with making online threats “relating to New Year’s Eve” festivities in Sydney, police said Friday.

The arrest follows police raids across the southern city of Melbourne a week ago, which authorities said foiled an Islamic State-inspired plot to attack prominent sites in the city Christmas Eve.

Damien O’Neil was arrested late Thursday and refused bail by a court Friday. He was charged under criminal laws relating to suicide or encouraging suicide, not terrorism laws, police said in a statement. Police did not reveal his nationality.

O’Neil was acting alone and had “no links to any cultural groups,” New South Wales state acting Deputy Commissioner Frank Mennilli told reporters in Sydney Friday.

“He did post on social media a number of threats of some possible activity that he could be undertaking,” Mennilli said, without giving any further details.

Australia, a staunch U.S. ally that sent troops to fight in Afghanistan and Iraq, has been on heightened alert for attacks by home-grown radicals since 2014.

Security in Melbourne was bolstered after last week’s raids and more than 2,000 police will patrol harborside locations in a major security operation in Sydney on Saturday, where tens of thousands of revelers are expected to ring in the new year.

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