As CBS News Correspondent Kimberly Dozier reports, Zarqawi's group has already been targeting anyone involved in setting up the polls.
His Sunni followers are among the top suspects in a deadly car bombing Monday, which narrowly missed killing Iraq's top Shiite candidate.
The car bomber instead killed 15 when he was stopped at the gate of the home of Abdul Aziz al-Hakim, leader of the Supreme Council for the Islamic Revolution in Iraq. The bomber detonated his explosives when guards blocked the way.
At least 50 were wounded in the explosion, which shook Baghdad's Jadiriyah district and sent a cloud of smoke billowing into the sky, police Capt. Ahmed Ismail said. Thirty-two cars on the street were destroyed or damaged. Al-Hakim, who was inside, was not hurt.
Al-Hakim heads the 228-candidate list of the United Iraqi Alliance, which includes parties and individuals from all Iraqi ethnic and religious groups but is dominated by Shiites, who account for about 60 percent of the country's population. Backed by Iraq's top Shiite cleric, Grand Ayatollah Ali al-Sistani, the coalition is widely expected to dominate the postelection constitutional assembly and play a key role in formulating Iraq's new national charter.
The two events underlined the difficulties that the insurgency is causing for Iraq's interim government and the U.S.-led military coalition in trying to hold credible national elections — the first free ballot since the overthrow of the monarchy 46 years ago.
In other developments:
In urging a boycott of the election, the voice on the Al-Jazeera tape described al-Zarqawi as the "emir" of al Qaeda in Iraq and called on Muslims there "to listen to him." Last month al-Zarqawi declared allegiance to bin Laden and changed the name of his group, which is responsible for numerous car bombings and beheadings of foreign hostages in Iraq, to Al Qaeda in Iraq.
Continuing attacks and intimidation have led senior Sunni political and religious leaders to call for a postponement of the vote until the insurgency is brought under control.
The Iraqi Islamic Party said its decision to pull out of the race did not mean it would not take part in a future ballot. "The party's desire is to take part in the future, should the requirements for its success be available," it said.
Party Secretary General Tarek al-Hashemi acknowledged the withdrawal would leave minority Sunnis underrepresented in the assembly elected Jan. 30, but added: "We believe when a house is on fire, you should first put out the fire before working on decorating and arranging it."
Shiites comprise by far the biggest community in Iraq, with Sunni Arabs and ethnic Kurds making up 20 percent each. Many people in Iraq and abroad fear the legitimacy of the election will be brought into question if Sunnis refrain from voting.
Shiite political and religious leaders also have sharply criticized the U.S.-led response to the insurgency, saying Iraqis themselves would have been more effective in countering the mainly Sunni insurgency. But Shiite leaders also strongly back going ahead with next month's vote even though they have been repeatedly targeted by the insurgents since the ouster of Saddam Hussein.
Since the modern Iraqi state was set up by British colonialists in the aftermath of World War I, it has always been dominated politically and economically by the Sunni minority, and Shiite leaders are eager to translate their numerical superiority into political power.
Monday's suicide attack was the second aimed at a leader of al-Hakim's party on the same block. On Nov. 7, a car bomb exploded near the home of Iraq's finance minister, Adil Abdel-Mahdi, killing one of his guards but missing Abdel-Mahdi.
After Monday's blast, al-Hakim denounced the interim government's security apparatus, claiming it had been infiltrated by Saddam loyalists.
"We hold the Iraqi government responsible for such criminal acts. This government has adopted the same wrong policies that were adopted by the occupation forces in dealing with security," he told Iraq's Al-Furat Television.
The residence where al-Hakim has his home and office was previously the house of Tariq Aziz, one of Saddam's senior aides who has been in prison since shortly after the U.S.-led invasion last year.
Al-Hakim's elder brother, Ayatollah Mohammed Baqir al-Hakim, also a Shiite cleric and a former leader of the party, was killed by a suicide bomber in August 2003. Both brothers opposed Saddam from exile in Iran before returning to Iraq after last year's U.S.-led invasion.
In other developments, two U.S. soldiers were killed by separate roadside explosions, the military said Monday.
One soldier died and a second was wounded when a bomb hit a patrol in Samarra, 60 miles north of Baghdad. Another soldier was killed and four were wounded by a bomb in Baghdad.
The latest casualties brought to at least 1,325 the number of U.S. troops who have died in Iraq since the beginning of the war in March 2003.