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A teenage girl and a 20-year-old man are accused of sending money to the so-called Islamic State from Australia.
The pair are expected to be charged with financing terrorism, which carries a maximum penalty of 25 years' jail.
The man was previously arrested during Australia's largest counter-terrorism raids in September 2014.
He is the 14th and final person to be put before the courts as a result of the mass arrests, police said.
NSW Police Deputy Commissioner Catherine Burn reiterated concerns about the girl's age.
"I previously said that it was disturbing that we continue to deal with teenage children in this environment. And today's arrest hasn't altered that position," she told reporters in Sydney.