Gunmen ambushed a convoy of trucks carrying construction material to U.S. military north of Baghdad Sunday, killing four Iraqi drivers. Search crews found the wreckage of a German plane in northern Iraq with the six people on board dead.

A police general also died in a roadside bombing in northern Iraq as violence continued a day after 20 people, including a U.S. soldier, were killed in a spate of bombings and shootings.

A prominent Kurdish politician, meanwhile, said talks between Kurdish and Shiite leaders on forming a new government are "not going well" because of major policy differences. That could delay formation of a new government and any drawdown of U.S. forces.

The plane was 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 area near the border between Iran and Iraq.

Shahou Mohammed, the regional administrator in Sulaimaniyah, said the wreckage was found near Boushin, northeast of Sulaimaniyah, 160 miles northeast of Baghdad, after villagers reported the crash.

He said searchers, who were in radio contact with him, found six bodies on board.

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."

He said the site was at an elevation of about 4,200 feet and recovery efforts would continue Monday.

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

The ambush occurred near Nibaie, about 35 miles north of the capital, police Lt. Khalid al-Obaidi said. The area has been the scene of several ambushes and roadside bombings in the last few days.

In Baghdad, a car bomb exploded Sunday afternoon near a Shiite political office in the Jadiriyah district, killing two people, including a policeman, and wounding five, three of them police, officials said.

Minutes later, a suicide bomber detonated explosives strapped to his body at an Iraqi army checkpoint protecting the Defense Ministry in central Baghdad. Three civilians were injured, police said.

Also Sunday, police found bodies of three men — bound, blindfolded and shot execution-style — in Baghdad's Shiite stronghold of Sadr City. They appeared to be the latest victims of sectarian tit-for-tat killings, which have sharpened religious tensions as Iraqi politicians try to form a national unity government following the December parliamentary elections.

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

Sheik Ismaiel al-Badri of the Association of Muslim Scholars said more than 300 Sunni Arabs have been assassinated in Baghdad over the past four months. The figure could not be independently confirmed.

"What's going on in Iraq is a dangerous human crisis and its impact will cross Iraq's borders if no one puts a stop to it," al-Badri told reporters at Umm al-Qura mosque in the capital.

He said the killings were occurring "as if the government security forces and militias are racing against time to claim as much as they can from its rivals who oppose it."

Al-Badri described "the sectarian cleansing" carried out by Interior Ministry-led militias "is the real barbaric terrorism."

The Interior Ministry has denied running or sanctioning sectarian death squads but it has announced an investigation into allegations of Shiite death squads in police ranks after U.S. troops arrested 22 policemen preparing to kill a Sunni Arab last month.

In political developments, Mahmoud Othman, a member of the Kurdish negotiating committee, said talks between the Kurds and Shiites were facing problems over several issues, including a proposed oversight council and the system for taking government decisions.

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

Under the new constitution, formation of the new government should be complete by mid-May, although some U.S. officials believe the process could take longer.

Shiite officials refused to comment publicly on Othman's assessment, although some familiar with the talks acknowledged difficulties.

The Shiites control 130 of the 275 parliament seats and the Kurdish Coalition has 53. The two groups were partners in the outgoing government.

If they cannot reach an agreement, it is less likely that a deal can be struck with the two Sunni Arab parties, which together hold 55 seats. Police Brig. Gen. Hatim Khalaf and his driver were killed when a roadside bomb exploded 20 miles southwest of Kirkuk, police said. Khalaf was the chief of the operations center for the police in Kirkuk, headquarters of Iraq's northern oil-producing center.

More than 1,000 students at Diyala University marched through the streets of Baqouba to the governor's office Sunday to protest the caricatures of the Prophet Muhammad, which first appeared in a Danish newspaper in September and have been reprinted in several European dailies. The students also were protesting a recent video showing British forces beating Iraqi youths during a January 2004 protest in Amarah.

Also Sunday, Australia said it would probably not withdraw its troops protecting Japanese reconstruction teams in Iraq even if the Japanese leave. Defense Minister Brendan Nelson said Australian forces could redeploy elsewhere.