With less than a month to go, the US military wants to minimise last-minute dangers and has paid tribal fighters cash to help provide a safe exit from Iraq after more than eight years of war.

Much of the mighty US military machine is leaving Iraq by heading south to Kuwait down the main highway, a tempting target for Iran-backed militants.

From Contingency Operating Base Basra, to the north of the border with Kuwait, Colonel Douglas Crissman of the US army commands American forces in four southern Iraq provinces.

Under his supervision, soldiers prepare to hand the base to Iraqi forces in the coming days, but they also oversee security for US personnel and equipment slowly making their way down the road.

"We are continuing our mission and securing paths for our sisters and brothers," Crissman said, referring to US soldiers and personnel.

Fewer than 10,000 US military personnel are still in Iraq, while five bases still remain to be handed over.

"We managed to get back... relations with more than 20 tribal sheikhs," the colonel said.

Tribal sheikhs are responsible for the safety of the highway "and that's why we pay them," he said.

The strip of highway known as T6 runs 400 kilometres (250 miles) from Diwaniyah 160 kilometres south of Baghdad to near Basra, and then continues on to Kuwait.

The road travels through desert and farmland but very few villages, raising the risk of attack.

In the case of a bombing, the colonel said: "We call that sheikh and say: 'Hey, what happened? This is your responsibility and we are paying you for that'."

With the end of year pull-out date approaching, the United States accuses Iran of fomenting an upsurge in violence against Americans.

In June, 23 soldiers were killed in the deadliest month in three years for the US military.

Turning to tribal protection is not a new tactic.

The insurgency that quickly followed the US-led invasion of 2003 was quashed in part thanks to the Sahwa militia forces, anti-Al-Qaeda fighters who fought alongside the Americans and were paid by them, beginning in 2006.

Similar methods were implemented around Diwaniyah, said Abu Mohammed al-Juburi, a tribal chief in the area.

"At the end of 2007, groups were formed to protect the roads... in agreement with US forces," he said.

"Salaries went from 500 to 700 dollars a month, paid by the Americans," Juburi said.

However, Juburi maintained that the system was no longer in place, even though this may have been because of the sensitivity of the issue of cooperating with the US military.

He said that since 2008, protection of the roads has been handed over to the provincial and district authorities that take their orders from the Iraqi military and national police.

The tribal fighters are now paid by the Iraqi authorities, Juburi said.