SYDNEY - An Australian nurse accused of giving medical assistance to the Islamic State militant group fighting in Syria appeared in a Sydney court on Saturday after surrendering to authorities in Turkey, police and media reports said.

Adam Brookman, 39, was arrested after in arriving in Sydney overnight.

"The man voluntarily surrendered himself to Turkish officials in Turkey on Tuesday, 21 July," a police statement said. His travel back to Australia had been negotiated with Australian government and international agencies, it said.

The police statement did not specify charges but said his arrest was connected with "his alleged involvement in the conflict in Syria."

Brookman, a father of five, has told Australian media he went to Syria on a humanitarian mission and had been forced to join the militant group after he had been wounded.

He will be moved to Melbourne at the request of an anti-terrorism task force, media reports said. Brookman did not speak as he appeared in the Sydney court via video link on Saturday.

Australia is on high alert for attacks by radicalized Muslims, including home-grown militants returning from fighting in the Middle East. It has raised its threat level to "high" and launched a series of high-profile raids in major cities.

Australian Prime Minister Tony Abbott has said at least 70 Australians were fighting in Iraq and Syria, backed by about 100 Australia-based "facilitators."

Abbott has secured a raft of new security powers in recent years, expanding domestic spying capabilities and proposing to strip citizenship from dual nationals accused of committing violent militant acts.