An Al Qaeda (search) lieutenant in custody in Iraq has confessed to masterminding most of the car bombings in Baghdad, including the bloody 2003 assault on the U.N. headquarters in the capital, authorities said Monday.

Sami Mohammed Ali Said al-Jaaf (search), also known as Abu Omar al-Kurdi, "confessed to building approximately 75 percent of the car bombs used in attacks in Baghdad" since the Iraq war began, according to the interim Iraqi prime minister's spokesman, Thaer al-Naqib.

A government statement said Al-Jaaf was taken into custody Jan. 15 and was responsible for 32 car bombings, including the bombing of the U.N. headquarters that killed the top U.N. envoy in Iraq, Sergio Vieira de Mello, and 21 other people.

The suspect, a top lieutenant of al-Qaida's Iraq leader, Abu Musab al-Zarqawi (search), also built the car bomb used to attack a shrine in the Shiite holy city of Najaf that killed more than 85 people, including Ayatollah Mohammed Baqir al-Hakim, in August 2003, the statement said.

It said he also assembled the car bomb used in May to assassinate Izzadine Saleem, then president of the Iraqi Governing Council.

Two other militants linked to al-Zarqawi's terror group also have been arrested. They included the chief of al-Zarqawi's propaganda operations and one of the group's weapons suppliers, the government statement said.

The government offered no evidence to support its claims, and the announcement followed a series of car bombings, kidnappings and assassinations of Iraqi security personnel, all of which have lowered public morale as the nation prepares for elections next weekend.

Since June 28, when the interim Iraqi government took power, there have been 202 car bombings across Iraq, including 70 in the Baghdad area, according to an Associated Press tally. The attacks have killed 1,061 people and injured 2,753.

Prime Minister Ayad Allawi has been promising to crush the insurgency and restore public order if he holds onto his job in the new government.

In the latest attack, a suicide bomber blew up a carload of explosives Monday outside the headquarters of Allawi's party, wounding at least 10 people in the latest blast claimed by al-Qaida in Iraq. The violence raised fresh fears about the safety of voters in Sunday's national elections, which Sunni Muslim insurgents have threatened to sabotage.

Al-Zarqawi has been trying to incite Sunni Arabs against the Shiite majority, playing on Sunni fears that the elections will spell the end of their privileged position in Iraq.

Monday's car bombing struck at a police checkpoint near the offices of Allawi's party, the Iraqi National Accord. Police said the guards opened fire moments before the blast, a thunderous explosion that reverberated throughout the city center.

Eight policemen and two civilians were wounded, according to Dr. Mudhar Abdul-Hussein of Yarmouk Hospital. It was the second suicide attack on the office this month.

In an Internet posting, al-Qaida in Iraq said the attack was carried out by "one of the young lions in the suicide regiment" against the "agent of the Jews and the Christians."

An audiotape posted on the Internet a day earlier, purportedly from al-Zarqawi, declared "fierce war" on democracy and said anyone who takes part in the elections would be considered "an infidel."

The authenticity of the tape could not be verified. Al-Zarqawi's group has been behind many car bombings, beheadings, assassinations and other attacks in Iraq. The United States has offered a $25 million reward for his capture or death — the same amount as for Al Qaeda leader Usama bin Laden.

Many Sunnis are expected to boycott Sunday's elections, either to express opposition to the process or for fear of reprisals. Shiites and Kurds are expected to vote in huge numbers.

Iraqis are to choose a 275-member National Assembly and legislatures in each of the 18 provinces. Voters in the Kurdish-ruled area of the north will also elect a new regional parliament.

Faced with discontent in the Sunni community, politicians running on a ticket endorsed by Shiite clerics, the United Iraqi Alliance, sought Monday to dispel fears that they would impose a hard-line Shiite state. Hanin Mohammed Qaddou, a Sunni Muslim on the ticket, said religious rule was "not part of the program and it will not be in the near future."

Shiite leaders also promised not to seek revenge for attacks by Sunni extremists.

"We believe that we have no justifications, whether religious or political, to escalate the situation and enter into the civil war quagmire because it means the Balkanization of Iraq or the Lebanonization of Iraq," said Khudayer al-Khuzai of the Islamic Dawa Party-Iraq.

Iraqi officials have announced stringent security measures to protect voters, including closing the borders, extending the hours of curfew and banning private vehicles. In addition, the 170,000 multinational troops, most of them American, have stepped up security operations, rounding up hundreds of suspected insurgents.

Fighting also raged Monday near the international airport, preventing two Jordanian passenger planes from landing, and sporadic explosions rumbled across the capital. The flight cancellations stranded many travelers, including eight Chinese construction workers who were freed by their Iraqi kidnappers this weekend.