BAGHDAD, Iraq - Two suicide car bombers struck within a minute of each other just a half-mile apart in south Baghdad shortly before noon today, killing at least seven policemen and raising the day's bombing death toll in the capital to at least 31, police said.

Earlier today, a suicide car bombing killed sixteen policemen and five civilians in the same neighborhood, signaling a new round of violence one day after residents suffered through Baghdad's bloodiest day of the war.

At least 160 were killed and 570 wounded Wednesday in more than a dozen bombings, which the terror group Al-Qaida in Iraq claimed responsibility for. Many of the victims were day laborers lured by a suicide attacker posing as an employer. There was no immediate claim for today's bombings.

Al-Qaida's leader in Iraq, Abu Musab al-Zarqawi, purportedly declared "all-out war" on Shiites, Iraqi troops and the government in an audiotape posted Wednesday on an Internet site known for carrying extremist Islamic content.

Also today, three civilians were killed when a roadside bomb struck a Ministry of Industry bus in eastern Baghdad. Thirteen were injured, said police Lt. Col. Ahmed Abbod.

U.S. forces and insurgents, meanwhile, reportedly clashed in the troubled western town of Ramadi, a militant stronghold on the main road to neighboring Jordan. A Web posting purportedly from Al-Qaida in Iraq said its forces had engaged the American military in the predominantly Sunni city of about 800,000.

In claiming it carried out the Wednesday attacks, Al-Qaida said it was retaliating against the Iraqi-U.S. rout of militants from their base in Tal Afar, the northern city near the Syrian border.

Today's attacks began at 8 a.m. Four hours later the twin bombing boomed out across Baghdad.

"There was just one minute and one kilometer between the two car bombs," said police Capt. Firas Gaiti. He said at least seven policemen died and 10 were wounded.

In the ethnically mixed city of Kirkuk, 180 miles north of Baghdad, insurgents detonated a roadside bomb next to a passing patrol, killing two police officers and wounding four, said Col. Anwar Hassan, head of the local security unit.

U.S. and Iraqi troops in Ramadi, an insurgent stronghold 70 miles west of Baghdad, came under mortar attack this morning as armed militants roamed the streets, police Capt. Nasir Alusi said.

All shops in the town - a major insurgent stronghold - were closed and the streets were empty as automatic gunfire echoed through the town's industrial zone, Alusi said.

The al-Zarqawi tape Wednesday was a clear attempt, coming on the heels of the attacks, to create a climate of fear, sow deeper sectarian discord and scare Iraqis away from the Oct. 15 referendum on a new constitution.