Iraqi leaders have trumpeted a joint Arab-Kurdish "Golden Lions" security unit in the disputed northern city of Kirkuk but key issues remain over its funding and expansion.
American troops, who were key to the force's formation in early 2010, have taken a back seat in the combined unit's operations ahead of the planned year-end US pullout.
Senior American officers have voiced concern that the force's mandate has become wide and too complex, and questioned if officials in Baghdad and the Kurdish regional capital Arbil can resolve crises without US mediation.
"I'm confident that at the very low tactical level, the government of Iraq and KRG (Kurdistan regional government) security forces work well together, primarily because politics aren't involved at the checkpoint," said Brigadier General Jim Pasquarette, deputy commander for US forces in north Iraq.
He quickly added: "I think you can put a US army platoon and a North Korean platoon on a checkpoint together, and a week later, they'd be playing cards and having a good time together."
Following proposals floated in 2009, the US military began training Iraqi soldiers, policemen and Kurdish peshmerga fighters in combined units across a swathe of disputed territory centred around Kirkuk in the country's north.
While Kurdish authorities want the area incorporated into their autonomous region in Iraq's north, officials in Baghdad are strongly opposed.
At the time the force was initially mooted, analysts and officials feared tensions could develop into open conflict along what the International Crisis Group dubbed the "trigger line."
Since early 2010, US forces manned checkpoints alongside Iraqi army and peshmerga members in Nineveh and Diyala provinces. In Kirkuk, the tripartite force conducted patrols and raids, while American soldiers ran checkpoints with Iraqi policemen.
Earlier this month, however, US forces pulled out of the checkpoints, and will also soon relinquish leadership in the three provincial coordination centres.
According to Colonel Michael Bowers, strategist for the top US general in north Iraq, violent incidents in the area have dropped since early 2010.
And what was initially pitched as a limited plan to build cooperation between primarily Arab forces and their Kurdish counterparts, has expanded markedly, particularly in Kirkuk.
Once a company-sized unit of around 100 members, it has now become a battalion of around 350, primarily focused on manning six checkpoints in the city, and there is talk of further expansion to a brigade of more than 1,000 members.
But key hurdles remain.
For one, the battalion is still funded and supplied on an ad hoc basis.
"We are facing challenges, because this joint force is new and contains three groups," said Colonel Salah Adin Saber, an Iraqi police officer and the battalion commander.
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"Among the challenges are logistics support, and the supply of fuel and vehicles."
According to US Lieutenant Colonel Joseph Holland, Saber "has got to go round and get everybody to provide some resources."
"What they need is a separate budget line from Baghdad ... so that they don't have to continually shell out cash to make this thing work."
He added the current system was "not the preferred solution."
American commanders also fret that unnecessary complexity has been added by putting the battalion on checkpoints, rather than local policemen, whose force is in charge of security in Kirkuk.
"Instead of a clean, simple solution, we have a more complex solution, so that everybody has a person there," said Colonel Michael Pappal, commander of the 1st Brigade Combat Team, 1st Infantry Division located at a US base on Kirkuk's outskirts.
Pappal said while local leaders had agreed to let Iraqi policemen run the checkpoints when the US pulled back, "the other levels up didn't think that was the solution."
Holland, meanwhile, warned that Saber had "very few Iraqi army and peshmerga available to do patrolling.
"He can't do both tasks (checkpoints and patrols) at the same time with the current battalion that he's got."
In addition to lying at the centre of the disputed territory, Kirkuk province is also rich in oil and home to a wide variety of ethnic groups.
Little progress has been made, though, over competing claims to Kirkuk, with oft-cited Iraqi constitution article 140, which calls for a referendum to decide Kirkuk's fate, unimplemented.
As a result, tensions remain, rising markedly in late February when, amid nationwide protests, peshmerga forces shifted their fighters southwest towards Kirkuk city in what they said was a move to protect it.
The Iraqi army and officials in Baghdad repeatedly called for the Kurdish forces to return to their original positions amid fears of fighting. The peshmerga eventually pulled back in late March.
"They were mad at each other about it all," Pappal said, noting weekly meetings between security leaders in Kirkuk "had fallen apart at that point."
"The US got everybody working back together again, got people back where they belonged, and got it all resolved."
American forces are set to withdraw from Iraq by the end of the year, though Baghdad has agreed to open negotiations to maintain a training mission beyond that time. Officials on both sides note, however, that it remains possible no deal is reached.
The absence of any political agreement ahead of the withdrawal has made some Kirkuk politicians fearful.
Hassan Toran, head of the local provincial council, noted that "lack of a common political and security vision... is a source of concern."