US President Barack Obama's envoy charged with building the coalition against the Islamic State of Iraq and the Levant (ISIL) armed group has said that the growth of the group has global implications and if unchecked its fighters could "wreak havoc on the progress of humanity".
Retired General John Allen told a conference in Doha, the Qatari capital, on Wednesday that the armed group was not merely an Iraqi problem or a Syrian problem but "a regional problem trending towards global implications".
Allen said it was critical that all anti-ISIL forces in Iraq fell under Iraqi government authority and that the task of countering the flow of foreign fighter into the region could not rest with Turkey alone.
Turkey's borders with Syria and Iraq were the "last line of defence", he said.
On Tuesday, speaking to reporters before a meeting of foreign ministers from the international coalition fighting the group, Haider al-Abbadi, Iraq's prime minister, said that his country needs more global support to counter ISIL's advance.
Discussing the situation in Syria, Allen said President Bashar al-Assad should have no role in any long-term solution to Syria's conflict.
Allen said that there was a "very energetic" discussion among a number of countries about how to bring about a political transition in Damascus, but that such a solution would not include Assad, who has been fighting various armed groups since 2011.
ISIL has made several recent gains, conquering both the Iraqi city of Ramadi and the historic Syrian city of Palmyra.
More than 4,100 air strikes by the US-led coalition have failed to stem gains by ISIL fighters.