SYDNEY (REUTERS) - Australia will send an additional 300 soldiers to help train Iraqi forces fighting Islamic State in Iraq and Syria (ISIS) militants, Prime Minister Tony Abbott said on Tuesday, following a request from the United States to contribute to an international training coalition.

Australia last year committed a 600-strong force comprising some 400 airforce personnel and 200 special forces soldiers to help fight ISIS.

The new Australian troops will join around 140 New Zealand Defence Force members and be based at Taji, north-west of Baghdad, Abbott told reporters.

"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," Mr Abbott said.

Australia is on high alert for attacks by radicalised Muslims or home-grown militants returning from fighting in the Middle East.

In December, two hostages and a radical self-styled sheikh who had sought to align himself with ISIS were killed in a Sydney hostage siege.

"The government's decision has the support of the Prime Minister of Iraq and it responds to a formal request from the United States to contribute specific Australian Defence Force capabilities to this international coalition," Mr Abbott said.