Sydney - Australia announced on Tuesday it will send another 300 troops to Iraq in a joint mission with New Zealand to help train local forces fighting ISIS.
The decision follows Wellington last week deciding to deploy some 140 soldiers on a non-combat mission to boost the Iraqi military's ability to fight the jihadists.
Prime Minister Tony Abbott said the decision followed a formal request from the Iraqi and US governments.
"I want to stress that we haven't taken this decision lightly. Ultimately, it is Iraq that must defeat the death cult [ISIS] but we do not want to leave the Iraqis on their own," he told reporters in Canberra.
"We are naturally reluctant as a peace-loving people to reach out to far-away conflicts but, as we know, this conflict has been reaching out to us for months now."
Some 170 Australian special forces are already in Iraq helping to train government troops, and Abbott said it was in his country's national interest to boost their presence.
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"I stress, the death cult has been reaching out to our country with about 100 Australians fighting with Daesh [ISIS] and other terrorist groups in Syria and Iraq," he said.
"About another 150 here at home are supporting these extremists so this commitment is a matter of domestic as well as international security, and I stress this is absolutely and utterly in Australia's national interests to do this."
The Australian and New Zealand troops are to be based at a military base in Taji, north of Baghdad, from May.
Since August 2014, the US military -- along with allies including Australia -- has been conducting a campaign of air strikes against the jihadists in Iraq and Syria.
Australia's role is restricted to aerial support, training, advice and intelligence.
Australia contributed about 2 000 troops to the US-led coalition's war in Iraq from March 2003, until they withdrew in 2009. None died in combat or on operational duty during that deployment.