WASHINGTON - Defence Secretary Ashton Carter has acknowledged that the US effort to train Iraqi forces to battle Islamic State in Iraq and Syria (ISIS) militants is behind schedule because too few Iraqis have signed up to fight the militants.

"We simply haven't received enough recruits," Mr Carter told the House Armed Services Committee on Wednesday. "Of the 24,000 Iraqi security forces we had originally envisioned training at our four sites by this fall, we've only received enough recruits to be able to train about 7,000, in addition to about 2,000 counter-terrorism service personnel."

US Army General Martin Dempsey, the outgoing chairman of the Joint Chiefs of Staff, reiterated that victory against the extremists requires a reinvigorated, multi-sectarian coalition of Sunni, Shi'ite and Kurdish soldiers fighting on their nation's behalf.

"This has to be them," said Gen Dempsey, when pressed by a lawmaker on whether the US faces a quagmire or stalemate. He disagreed with increasing ground forces "to stiffen the spine of local forces".

Meanwhile, an arrest warrant was issued yesterday for an Australian-trained doctor who appeared in an ISIS propaganda video which urges other medical professionals to join the militants, police said.

Tareq Kamleh was shown in the slick video, uploaded to YouTube in April, identifying himself as Abu Yusuf and explaining that he travelled to the city of Raqa in Syria to use his medical skills for the ISIS cause. Police said he was an Adelaide-trained doctor who has worked in hospitals in South Australia, Queensland and the Northern Territory.

BLOOMBERG, AGENCE FRANCE-PRESSE