Prime Minister Tony Abbott has confirmed that Washington made a "general request" to Australia for more military help in Iraq and has declared that the beheading of a second American journalist "abundantly justifies" intervention.

In remarks on Wednesday that offer the clearest indication yet that Australia will become more involved in military action in Iraq, Mr Abbott revealed that the government had been asked whether it would, in principle, contribute to a wider, US-led military campaign.

"We have received no specific request to engage in actual military action against ISIL," he said, using the alternative name for the brutal Islamic State group. "Nevertheless, we have received a general request and we are considering what we may be able to make available."