By Colin Packham
SYDNEY, Sept 1 (Reuters) - Australia will expand its military action against the Islamic State militant group in Syria and Iraq after amending its domestic laws, Prime Minister Malcolm Turnbull said on Thursday.
Australia joined the U.S-backed coalition against Islamic State in September 2014, and has steadily increased its military participation against the group that has repeatedly called for attacks against the United States and other Western countries.
However, Turnbull said Australia's role had been hamstrung by differences between domestic and international law, a loophole that his government would close with new legislation.
Australian law currently only allows the targeting of people who were playing an active role in hostilities, which Turnbull said was more restrictive than international law.
"This legal risk posed a major challenge to the effectiveness of our operations. It meant that the [Australian Defence Force's] targeting base in Iraq and Syria was restricted, and we could not operate as freely as our coalition partners," Turnbull told the Australian parliament.
Turnbull said military operations could expand to target "a broader range" of Islamic State combatants once the law was changed.
In addition to outlining the expansion of its offshore response to the rising threat of Islamic State, Turnbull said his government would also press ahead with measures to combat domestic acts of terror.
A staunch U.S. ally, Australia has been on heightened alert for attacks by home-grown radicals since 2014, having suffered several "lone wolf" assaults, including a cafe siege in Sydney in which two hostages and the gunman were killed.
In July, Australia proposed legislation to indefinitely detain people convicted of terrorism-related charges if it felt they posed a danger to society upon their released. legislation would be introduced to parliament next week, Turnbull said.
Turnbull also flagged stronger surveillance of potential Islamic State supporters in Australia.
He said approximately 200 people were being investigated in Australia for providing support to individuals and groups in the conflict in Syria and Iraq.
"There are still people outside our country, and some within it, who hate the freedoms that we enjoy and would seek to threaten them and undermine them with violence," said Turnbull.