The statement followed a deadly day in Baghdad, where explosions throughout the capital killed more than 160 people.
The speaker on the tape, introduced as Abu Musab al-Zarqawi, also said his militant forces would attack any Iraqi it believes has cooperated with an ongoing U.S.-led offensive in the northern Iraqi city of Tal Afar.
"If proven that any of (Iraq's) national guards, police or army are agents of the Crusaders, they will be killed and his house will demolished or burnt, after evacuating all women and children, as a punishment," the voice said in the new tape that surfaced on an Internet site known for carrying extremist Islamist content.
The speaker on the tape, which could not be immediately authenticated, announced "all out war against Shiites everywhere. Beware, there will be no mercy."
A dozen explosions ripped through the Iraqi capital Wednesday, killing at least 160 people and wounding 570 in a series of attacks that began with a suicide car bombing that targeted laborers assembled to find work for the day. Al Qaeda in Iraq claimed responsibility.
The deadliest bombing killed at least 112 people and wounded more than 200 in the heavily Shiite neighborhood of Kazimiyah where the day laborers had gathered shortly after dawn.
Overnight Wednesday, 17 men were executed in a village north of Baghdad, which put the death toll in all violence in and around the capital Wednesday at 169 and the number continued to rise.
A senior American military official told The Associated Press he believed the rash of bombings was retaliation for the joint Iraqi-U.S. sweep through the northern city of Tal Afar in recent days to evict insurgents from their stronghold near the Syrian border. Al-Jazeera television quoted the al Qaeda as confirming that assessment.
Wednesday's carnage was believed to be the second worst since the U.S.-led invasion. On March 2, 2004, coordinated blasts from suicide bombers, mortars and planted explosives hit Shiite Muslim shrines in Karbala and in Baghdad, killing at least 181 and wounding 573.
Politicians immediately denounced the bombings. Husein al-Shahristani, deputy speaker of the National Assembly called the killings "barbaric and gruesome."
In recent developments: