Municipal workers in the Shiite holy city of Karbala found remains believed to be from a mass grave dating to 1991, when Saddam Hussein's regime put down a Shiite uprising in the south.

Also, more than 10,000 people marched through Baghdad in support of a national unity government of Sunnis and Shiites, while insurgent attacks killed six Iraqi policemen and two civilians in a fresh surge of violence.

The remains were discovered Monday and were sent for testing Tuesday in an effort to identify the bodies, said Rahman Mashawy, a Karbala police spokesman. He did not say how many bodies were found, and the police claim could not be independently verified.

Human rights organizations estimate that more than 300,000 people, mainly Kurds and Shiite Muslims, were killed and buried in mass graves during Saddam's 23-year rule, which ended when U.S.-led forces toppled his regime in 2003. Saddam and seven co-defendants are now on trial for the deaths of more than 140 Shiites after a 1982 attempt on Saddam's life in the town of Dujail, north of Baghdad.

Violence has increased across Iraq after a lull following the Dec. 15 parliamentary elections, with at least two dozen people — including two U.S. soldiers — killed in shootings and bombings Monday and 18 on Sunday.

Officials said insurgents were trying to deepen the political turmoil surrounding the contested vote. Preliminary figures have given a big lead to the religious Shiite bloc that controls the current interim government.

The new violence came as three opposition groups threatened a wave of protests and civil disobedience if fraud charges are not properly investigated. The warning came from the secular Iraqi National List, headed by former Shiite Prime Minister Ayad Allawi, and two Sunni Arab groups.

The demonstrators, some carrying photos of Allawi, marched in favor of a government that would give more power to Sunni Arabs and secular Shiites. Marches chanted "No Sunnis, no Shiites, yes for national unity."

"We're protesting to reject the elections fraud. We want to ask the government and the elections commission: 'Where did our votes go? Who stole them?'" said Abdul Hamid Abdul Razzaq, a 45-year-old barber.

Sen. Arlen Specter, R-Pa., visiting Iraq on Tuesday, said he met with the chief judge overseeing Saddam's trial. Specter said he was disappointed in how the court has allowed the former leader "to dominate" the trial.

"You have a butcher who has butchered his own people, a torturer who has tortured his own people," Specter said. "The evidence ought to be presented in a systematic way which would show that there's been quite an accomplishment in taking (Saddam) out as opposed to letting him be a blusterbun and control the proceedings."

Specter also said a U.S. general told him that recently announced U.S. troop reductions had been in the works since April and that more are on the way.

On Tuesday, clashes erupted between gunmen and Iraqi police in Baghdad, killing two policemen and two bystanders, Capt. Firas Keti said. South of Baghdad, a roadside bomb targeting a police patrol killed two officers, and gunmen in southern Baghdad killed another, police said.

Gunmen southeast of Kirkuk, 180 miles north of Baghdad, killed one police officer, Capt. Farhad Talabani said.

The U.S. military on Tuesday said two U.S. pilots died in a helicopter accident in western Baghdad. The accident was under investigation; the military said no hostile fire was involved.

A U.S. Army soldier assigned to the 2nd Marine Division, II Marine Expeditionary Force, died of wounds received on Monday after coming under fire while conducting combat operations in the town of Khaldiyah, 55 miles west of Baghdad, the military said.

Iraq's Electoral Commission said Monday that final results for the 275-seat parliament could be released in about a week.

Sunni Arab and secular Shiite factions are demanding that an international body review more than 1,500 complaints, warning they may boycott the new legislature. They also want new elections in some provinces, including Baghdad. The United Nations has rejected an outside review.

"We will resort to peaceful options, including protests, civil disobedience and a boycott of the political process until our demands are met," said Hassan Zaidan al-Lahaibi of the Sunni-dominated Iraqi Front for National Dialogue. He spoke in neighboring Jordan, where representatives of the groups have met in recent days.

The election commission considers 35 of the complaints serious enough to change some local results. But Farid Ayar, a commission official, said there was no reason to cancel the entire election.

He also said preliminary results from early votes by soldiers, hospital patients, prisoners and overseas Iraqis showed a coalition of Kurdish parties and the main Shiite religious bloc each taking about a third. Those nearly 500,000 votes were not expected to alter overall results significantly.

Preliminary results previously released gave the United Iraqi Alliance, the religious Shiite coalition dominating the current government, a big lead — but one unlikely to allow it to govern without forming a coalition with other groups.

Alliance leader Abdul Aziz al-Hakim traveled to the northern Kurdish city of Irbil on Tuesday to discuss the formation of a governing coalition with Jalal Talabani, Iraq's Kurdish president, and Massoud Barzani, president of the Kurdish region.

Al-Hakim's secretary Haitham al-Husseini said there would also be negotiations with Sunni Arabs. Al-Husseini said the Alliance has proposed distributing the top six Cabinet positions, the three-member presidency council and top three parliament slots among the political blocs.