A number of asylum-seeker children held in Australian mainland immigration detention centres are to be released, officials said Tuesday, although hundreds of others will remain locked up in offshore camps.

Australia will offer to resettle some 4,400 people fleeing violence in Iraq and Syria, Immigration Minister Scott Morrison said Sunday, adding the places had been freed up by success in stopping asylum-seeker boats.

Boat arrivals have all but dried up since Australia said it would refuse resettlement to any refugees arriving on unauthorized vessels, sending them instead to Papua New Guinea and Nauru in the Pacific.

Australia has carried out its first airdrop to refugees in northern Iraq, Prime Minister Tony Abbott said Thursday, joining a growing international effort to deliver humanitarian assistance.

"The mission was conducted by a RAAF C-130J Hercules delivering 10 pallets of badly needed supplies to Yazidi civilians trapped on Mount Sinjar by encircling ISIL forces," he said, referring to Islamic State militants, previously known as ISIL.

Prime Minister Tony Abbott has confirmed Australian planes will join humanitarian airdrops in Iraq and did not rule out the possibility of greater military involvement. 

Abbott, speaking in London after security talks, said Canberra was in discussions with international partners on how to protect displaced Iraqi civilians trapped on Mount Sinjar by jihadist Islamic State militants.

The United States and Australia agreed Tuesday to take concerns about the threat posed by jihadist foreign fighters in Syria, Iraq and elsewhere to the United Nations, U.S. Secretary of State John Kerry said.

"We intend to join together in order to bring this to the United Nations meeting this month and put it on the agenda in a way that will elicit support from the source countries as well as those countries of concern," Kerry said after joint security talks in Sydney.

The United States stressed Tuesday it welcomes the rise of China and wants to work constructively with Beijing as it signed a deal to deploy 2,500 Marines to Australia as part of its "rebalance" to Asia.

A shocking image of what is believed to be the young son of an Australian man holding a decapitated head in Syria shows how barbaric the Islamic State "terrorist army" is, Prime Minister Tony Abbott said Monday.

He made the comment while announcing Australia will likely join airdrops of supplies to Iraqi civilians besieged by jihadist IS militants on a barren mountain.

U.S. Secretary of State John Kerry on Monday warned Iraqi Prime Minister Nuri al-Maliki not to cause trouble as he threw his weight behind newly-elected President Fuad Masum to help fight Islamic militants.

His comments came after Maliki announced Sunday on state television he would be filing a complaint against Masum and as troops and police massed in the capital Baghdad.

A shocking image of what is believed to be the young son of an Australian man holding a decapitated head in Syria shows how barbaric the Islamic State "terrorist army" is, Prime Minister Tony Abbott said Monday.

He made the comment while announcing Australia will likely join airdrops of supplies to Iraqi civilians besieged by jihadist IS militants on a barren mountain.

United States Secretary of State John Kerry arrived in Sydney Monday for annual talks with close ally Australia, which an official said will range from the crisis in Iraq to security issues in Asia.

The centrepiece of the Australia-United States Ministerial Consultations (AUSMIN) on Tuesday is expected to be the signing of the framework for the rotational deployment of up to 2,500 U.S. Marines through the northern city of Darwin.