As the US president sends military advisers to Iraq, he notes the threat of Australian and European jihadists.
US President Barack Obama says he is "deeply concerned" about the terrorist threat Australian jihadists travelling to Syria pose on their return to Australia.
The president's comments come as the militant group, the Islamic State in Iraq and Levant (ISIL), also known as ISIS, extends its path of bloodshed in Iraq after crossing the border from war-torn Syria.
ISIL, through online recruitment videos, is enticing Australians and Muslims in other parts of the world to join their fight in Syria and Iraq.
The US is deploying up to 300 military advisers to asses the situation in Iraq and has been supporting moderate groups opposing ISIL and President Bashar Assad's regime in the fractured Syrian conflict.
"There is no doubt the problem in Syria is one that we have been paying a lot of attention to over the last couple of years as you see jihadists coming in from Europe and as far as Australia to get trained and then going back into their home countries," Obama said in an interview with CNN.
"This is something we have been deeply concerned about.
"Part of the reason we have been supporting a moderate opposition effort in Syria is to make sure there are forces countering some of the gains some of these extremist organisations have made inside of Syria."
There are reports of up to 300 Australians entering Syria to fight.
Australian Prime Minister Tony Abbott warned on Friday that jihadists who were "trained killers" and who "hate our way of life" must be stopped from re-entering the country.
In his strongest words yet about Australians fighting in Iraq and Syria, Mr Abbott said the government had "absolute determination" to prevent "returning jihadis".
"The important thing is to ensure that as far as is humanly possible, they don't come back into our country," he told Macquarie Radio.
"And if they do come back into our country, (that) they are taken into detention."