ANNE GEARAN

The Associated Press

ABOARD A U.S. MILITARY AIRPLANE (AP) -U.S. Defense Secretary Robert Gates said Wednesday he sees "some chance of a modest acceleration" in the pace of U.S. troop withdrawal from Iraq.

Gates, returning from a trip to Iraq, told reporters aboard his plane that perhaps one combat brigade would come out of Iraq ahead of schedule. He did not give a precise timetable.

U.S. officials had worried that last month's formal handover of control of Iraqi cities to Iraqi security forces might erode gains that had already been made. But Gates said Gen. Ray Odierno, the top U.S. general in Iraq, told him the security situation is better than expected.

President Barack Obama has announced plans to withdraw American combat forces from Iraq by Aug. 31, 2010. The bulk of the current 138,000 U.S. troops are expected to remain until Iraq's national elections, scheduled for late this year. Maintaining security for the balloting is considered a top priority by Odierno and other high-ranking Pentagon officials.

After the August 2010 deadline for withdrawal of combat forces, 30,000 to 50,000 U.S. troops will remain in advisory and training roles until the end of 2011.

Gates told reporters "there is at least some chance of a modest acceleration" in the pace of U.S. troop withdrawal.

Before leaving Iraq, Gates warned squabbling Kurds and Iraqi Arabs that they don't have much time to settle their differences and offered to help mediate before American forces leave.

Gates talked with Kurdish President Massoud Barzani and other leaders on their home ground in the Kurds' oil-rich, self-ruled area.

"We urged them to take advantage of our remaining time in Iraq to settle some of these disputed issues," Pentagon spokesman Geoff Morrell told reporters.

Gates "reminded his host that we have all sacrificed too much in blood and treasure to see the gains of the last few years lost due to political differences," Morrell said.

The secretary told Barzani he had delivered the same message to Iraqi Prime Minister Nouri al-Maliki in Baghdad on Tuesday.

The relatively affluent, peaceful Kurdish North is feuding with al-Maliki's government over its borders and resources. Gates met with Barzani, who claimed victory in a re-election vote last weekend that also saw large gains by an opposition slate, in Irbil, seat of the regional government.

Morrell said the U.S. military has advisers already serving as go-betweens for the Kurdish militia and Iraq's armed forces.

Gates told Barzani that the U.S. backs a set of United Nations recommendations to resolve some of the major disputes. Morrell would not characterize Barzani's response, except to say that Gates left the meeting "with the sense, just as he did in Baghdad, that the Kurds very much want to take advantage of our presence."

American military commanders say friction between Arabs and Kurds in northern Iraq is the greatest threat tosecurity in the country, overtaking the old Sunni-Shiite divide that threatened to push Iraq into civil war three years ago.

Odierno identified the tension in northern Iraq as the "No. 1 driver of instability."

"Many insurgent groups are trying to exploit the tensions," Odierno told reporters Tuesday. "We're watching very carefully to see that this doesn't escalate."

So far, American intermediaries are helping keep a lid on things, Odierno said. His deputy, Lt. Gen. Charles Jacoby, also pointed to friction between northern Iraq and southern Iraq as a main concern as the United States prepares to withdraw combat forces.

The Kurds have been locked in a dispute with Baghdad over control of oil resources and a fault line of contested territory in northern Iraq, particularly the flash-point city of Kirkuk. The disagreements have stalled a national oil law considered vital to encouraging foreign investment. U.S. officials have warned that Arab-Kurdish tensions could erupt into a new front in the Iraq conflict and jeopardize security gains elsewhere.

Separatist sentiment is high in Kurdistan, which gained autonomy after rising up against former Iraqi leader Saddam Hussein in 1991. The region was protected from his forces by a U.S.-British no-fly zone until Saddam's fall in 2003.

Kurdish leaders say they are committed to staying in a unified Iraq, particularly since an independence push could alienate neighboring Iran, Syria and Turkey, which have their own Kurdish minorities. But Iraqi Kurdish politicians must answer to the strong nationalist sentiment among Kurds.

Reformist candidates did better than expected against two established Kurdish political parties in weekend elections, adding to the uncertainty. The reformist slate, called Change, tapped into widespread frustration over alleged corruption and intimidation by the longtime ruling establishment.

Despite their internal differences, Kurds were united in their hard line in disputes with Iraq's Arabs.

Two mainstream parties have long dominated power in the northern region: the Patriotic Union of Kurdistan and the Kurdistan Democratic Party. They have been credited with keeping their region relatively prosperous and largely free of the violence that raged elsewhere in Iraq after the 2003 U.S. invasion.