WASHINGTON (AFP) - The US military's top officer said on Thursday that Iraqi forces had shored up their defences around Baghdad but would need outside help to eventually regain territory lost to Sunni militants.

General Martin Dempsey, chairman of the US Joint Chiefs of Staff, told a news conference that the initial impression from American military advisers on the ground was that Iraqi forces were not yet in a position to stage a major counter-offensive after being driven back by the Sunni extremists.

"If you are asking me will the Iraqis, at some point, be able to go back on the offensive to recapture the part of Iraq that they've lost... probably not by themselves," Gen Dempsey said.

But the Iraqi army's shortcomings did not necessarily mean the United States would have to take military action, he said.

"I'm not suggesting that that's the direction this is headed."

An Iraqi military campaign designed to roll back the Islamist militants would take time to develop and would have to be accompanied by clear signals from the Shiite-led government in Baghdad that it is ready to reach out to Sunni and Kurdish communities, the general said.

Gen Dempsey said "the first step in developing that campaign is to determine whether we have a reliable Iraqi partner that is committed to growing their country into something that all Iraqis will be willing to participate in.

"If the answer to that is 'no,' then the future's pretty bleak."

About 200 US military advisers have deployed to Baghdad with orders to assess the state of the Iraqi army and the threat posed by the Islamic State (IS) jihadists, who have seized control in areas north and west of Baghdad.

And nearly 500 US troops have been sent to Iraq to bolster security at the American embassy and parts of the Baghdad airport.