President Barack Obama says the United States will not hesitate to attack Islamic State in Syria and Iraq, and would allow "no safe haven" to the militant group.
"I can announce that America will lead a broad coalition to roll back this terrorist threat," he said in his televised address from the White House on Wednesday.
The jihadist group controls large parts of Syria and Iraq after a rapid military advance, and now runs a de facto government from the Syrian city of Raqqa, employing officials and administrators, the BBC reports.
Its fighters have become notorious for their brutality, beheading enemy soldiers and Western journalists on video.
Barack Obama said the United States will be joined by a "broad coalition", including allies already flying planes over Iraq, sending weapons to the Iraqi security forces and the Syrian opposition, and providing intelligence and humanitarian aid.
Combat troops will not be sent in the fight against IS, the president said. The US would send an additional 475 military advisers to Iraq, but they will not have a combat mission.
Strengthening the opposition in Syria was a counterweight to the group. The president called on Congress to give additional authorities and resources to train and equip opposition fighters in Syria while while aiming for a political solution to the war there.
Australian Prime Minister Tony Abbott said his country has not yet received a request from Washington for further military assistance in Iraq, but suggested it is likely to expand its involvement.
Australia is already supplying arms to Kurdish fighters in Iraq.
NZ supports move
New Zealand's Prime Minister said the Government supports US air strikes against Iraq, but it hasn't yet formed a view on air strikes against other countries.
John Key said today that, for the most part, it supports action against Islamic State.
"If the United States are taking action against that terrorist group then, for the most part, we would say that is in the interests of making a safer world, but specifically in Iraq we would support them."
Mr Key said the US is not asking for support from New Zealand and would be very surprised if they did.