A teenage girl and a 20-year-old man are accused of sending money to the so-called Islamic State from Australia.

Burn said police had had an interest in the 20-year-old for some time, and he was the 14th person who would be charged under Operation Appleby.

The pair are expected to be charged with financing terrorism, which carries a maximum penalty of 25 years' jail.

The pair were to face one charge each of getting funds to, from or for a terrorist organization.

Operation Appleby is investigating people suspected of being involved in domestic acts of terrorism.

A Sydney schoolgirl has been arrested by counter-terrorism police for allegedly sending money to a terrorist organisation.

Mr Atai and the girl, a Year 12 student, were arrested on Tuesday in Guildford Park moments after Mr Atai allegedly handed the girl a yellow envelope containing cash in bundles tied with elastic bands.

The two, both from Guildford, were arrested in Guildford this morning by the Joint Counter Terrorism Team Sydney as part of the ongoing Operation Appleby.

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"The 16-year-old girl is not somebody who is well-known to us, however it is disturbing that we are continuing to see a trend of teenage children involved in activities that they should really not be involved in at all".

She is said to have admitted in another conversation with the police source - who apparently ingratiated himself with the teenager's circle of associates by pretending to have a sister who wanted to travel to the Middle East - that "they had previously sent $10,000 a month ago".

Australian Federal Police Deputy Commissioner Michael Phelan said the latest arrests were not connected to any threat of an imminent attack.

The 16-year-old girl has not been on the police radar until now, Deputy Commissioner Catherine Burn said.

He also argued that she was at a "vulnerable" time in her life, had depressive and anxiety disorders and was a health risk.

"It's more this gives us the basis for figuring out the connection and it also gives us the basis for laying charges", he told Reuters.

"It is important that we try to identify all those things that might have been involved in her getting to this position".

Atai and the girl, who can not be named, will appear in court on Tuesday.