US Defense Secretary Robert Gates said during a visit to Iraq that the withdrawal of US combat troops from urban bases was paying off as Iraqi forces assumed the lead for the fragile security.

Gates is expected to touch on possible arms sales during the his visit and try to help bridge a deep divide between ethnic Kurds and Arabs that many fear may undermine security gains.

"Nobody's the boss or the occupier, or however you want to put it. But there's a real sense of empowerment by the Iraqis," Gates said of US-Iraqi cooperation following the June 30 deadline for pulling US combat troops out of city bases.

The withdrawal, a milestone in the plan to pull out all US troops of Iraq by the end of 2011, raised fears among some Iraqis that untested local forces would not be able to keep Iraq from sliding back into greater bloodshed.

"Less than a month into it, I'm really heartened," Gates told reporters after addressing US troops at the dusty, sun-baked Tallil air base on a sweltering summer day.

He said Iraq's security situation was "amazingly different" to that of his first visit to Iraq as US Defense chief in December 2006, at the height of the sectarian bloodshed that has killed tens of thousands of Iraqis since the 2003 invasion.

Gates met Iraqi Prime Minister Nuri al-Maliki and was due to hold talks with Defense Minister Abdel Qader Jassim.

He will visit the largely autonomous northern Kurdish region, which appears to be drifting farther from Arab leaders in Baghdad in an impasse over oil and disputed land, and is expected to meet Kurdish President Masoud Barzani.

Kurds vow to pursue their claims of areas like oil-producing Kirkuk as they assert greater control over hydrocarbon reserves.

The United States wants to prevent any clashes that might play into the hands of Sunni insurgents who would style themselves a bulwark against Kurdish encroachment.

"We're very much positioned now as kind of an honest broker," said a senior US Defense official, speaking on condition of anonymity.