On the second day of a visit to Iraq to reassure the war-torn country's leaders of continuing US support, Gates said: "I think that there is no question that the Kurds see their future as a part of a unified Iraq.

"The issue is the terms on which that goes forward -- that's negotiable," he told US troops at a forward base near the northern oil hub of Kirkuk.

"At this point all the evidence that we see indicates that they will work out those differences."

Kurds have long striven to expand their territory beyond its current three provinces to other areas where the population was historically Kurdish, leading to a dispute with Baghdad over a tract of land around Kirkuk province.

Article 140 of Iraq's constitution calls for a referendum to decide Kirkuk's fate, which Kurds have long wanted to make their capital, an aim strongly opposed by the province's Arab and Turkmen.

Kurdish reticence recently held up for a time the passage of a new electoral law governing a general election now set to be held in March.

Referring to Kirkuk and violence there following the 2003 US-led invasion, he told the troops it had "largely disappeared from the headlines. It doesn't mean that this theatre is not important. Your mission is still important..." and "will be increasingly important in the coming months."

The 115,000 US troops currently in Iraq are set to be reduced to 50,000 by the end of August, and will completely withdraw from the country by the end of 2011, as part of an agreement signed last year.

That timeline remains on track despite bombings in Baghdad on Tuesday that killed 127 people, Admiral Michael Mullen, the chairman of the Joint Chiefs of Staff, told reporters on Wednesday.

Gates reiterated that on Friday.

He said the commander of US forces in Iraq, General Ray Odierno, "is comfortable that he can stay with the plan that he has for the drawdown."

He emphasised the importance of finding out "what can be done to ensure that after the (March 7) elections there is a relatively quick formation of an inclusive government.

He pointed to the 2005 election which led to months of negotiations before a government was formed, saying that "really created an opening for the kind of sectarian violence" that exploded in 2006.