BAGHDAD, Iraq (AP) -- Iraqi political parties have run into obstacles in talks on a new national unity government, officials said Sunday, raising the possibility of a major delay that would be a setback to U.S. hopes for a significant reduction in troop levels this year.

In northeastern Iraq, search parties alerted by a shepherd found the wreckage of a German private plane that went missing in bad weather three days earlier with five Germans and one Iraqi on board. Iraqi and U.S. officials said there was no sign of survivors.

U.S. officials hope a new government that includes representatives of all Iraq's religious and ethnic communities can help calm violence by luring the Sunni Arab minority away from the Sunni-dominated insurgency so that U.S. and other foreign troops can begin to head home.

But prospects for a broad-based coalition taking power soon appeared in doubt after officials from the Shiite and Kurdish blocs told The Associated Press that talks between the two groups had revealed major policy differences.

The political parties have decided to negotiate a program for the new government before dividing up Cabinet posts - a step that itself is also bound to prove contentious and time-consuming.

Leaders from Iraq's Shiite majority oppose a Kurdish proposal to set up a council to oversee government operations, the officials said. Shiites also reject a Kurdish proposal for major government decisions to be made by consensus among the major parties rather than a majority vote in the Cabinet.

"If the position of the Shiite alliance is final, then things will be more complicated and the formation of the government might face delays," Kurdish negotiator Mahmoud Othman said.

Shiites believe the Kurdish proposals would dilute the power that Shiites feel they earned by winning the biggest number of seats in Dec. 15 parliamentary elections. But while Shiite parties control 130 of the 275 seats, that is not enough to govern without partners.

"Some parties are trying to undermine efforts to form a new government," Shiite politician Ammar Toamah said. "These blocs should not necessarily participate in government."

He also said the Kurdish coalition, which controls 53 seats, was pushing for a role for a secular group led by former Prime Minister Ayad Allawi, a Shiite whose party won 25 seats.

Many Shiites oppose Allawi because of his secular views and his role in the U.S. attack on Shiite militias in Najaf and Karbala in 2004 when he was prime minister.

Shiites and Kurds were partners in the outgoing interim government, and talks with Sunni Arabs are likely to be even more difficult because Sunnis refuse to brand all insurgents as terrorists. U.S. officials believe a strong Sunni role is essential if the new government is to undermine the insurgency.

Forming a new governing coalition is crucial to the U.S. strategy for drawing down its forces in Iraq. Under the new constitution, the new government is supposed to be complete by mid-May, but some U.S. officials believe the process could take longer.

The wrecked German plane had been en route to Iraq from Azerbaijan carrying five Germans and an Iraqi - employees of a Bavarian construction company - when it went missing during stormy weather Thursday night over the rugged mountains near the border with Iran.

Shahou Mohammed, the regional administrator in Sulaimani, said the wreckage was found about 25 miles northeast of Sulaimani by a Kurdish shepherd tending his flocks on a 4,200-foot ridge.

In Baghdad, U.S. Embassy official Peter McHugh said an American adviser who accompanied the Iraqi search team reported from the scene that the aircraft wreckage was scattered over a fairly large area and "there appear to be no survivors."

"Everything I've seen suggests this is an aviation accident," and was not the result of any "hostile intervention," he said.

A hard-line Sunni clerical group renewed accusations that the Shiite-dominated interim government is operating death squads to kill Sunni civilians and called on Muslim countries to support Iraq's Sunni community.