Australian police late Thursday (Dec 18) searched several properties across Sydney, reportedly as part of a ongoing counter-terrorism investigation but not related to the deadly cafe siege earlier this week, officials said.

New South Wales police said the raids were unconnected to the 16-hour standoff at a Sydney cafe on Monday that left the lone gunman, self-styled Islamic cleric Man Haron Monis, and two hostages dead, but would not provide further details about the operation.

"The (Australian Federal Police) and New South Wales police can confirm that they are conducting search warrants today in Sydney as part of an ongoing operation," a spokeswoman told AFP. "As this activity remains ongoing and to ensure the safety and security of the operation and members involved, it is not appropriate to provide further details at this time."

The spokeswoman could also not confirm local media reports that one of the homes raided had also been searched by police during large-scale counter-terrorism raids across the country in September. Australia raised its terror threat level in September on growing concern about militants returning from fighting in Iraq and Syria.

On Monday, a 25-year-old man was arrested as part of ongoing investigations into plans for an attack on Australian soil, the federal police said. A 22-year-old already facing a charge of preparing for a terrorist act was also charged with funding terrorism.

"Police will allege that men were key facilitators in the movement of funds that paid for Australians to travel to the Middle East to fight with the proscribed terrorist organisation, Islamic State," federal police said in a statement on Monday.

"Police allege the men made available to a terrorist organisation approximately A$15,000 (US$12,300) in funds in August this year." The 22-year-old will face a Sydney court Friday.