Abu Musab al-Zarqawi's terror network claimed responsibility for the attacks. Most of the casualties were Iraqi civilians. A large number were killed in simultaneous car bombings in the northern city of Mosul, but some also died as U.S. troops battled the guerrillas. At least 320 people were wounded, including 12 Americans.
U.S. officials had been warning of this very scenario — a new push to torpedo the June 30 transfer of sovereignty to an interim transitional government, reports CBS News Correspondent Kimberly Dozier.
The broad offensive — with violence in at least six cities — was the most extensive since attacks in early April. It showed a strength to the insurgency that appeared to surprise even U.S. officials who have been warning that guerrillas would try to sabotage the transfer of power.
The U.S. military responded with heavy firepower, dropping 11 500-pound bombs and a 2,000-pound bomb.
The assaults were launched in the morning, when black-clad guerrillas attacked police stations and government complexes in Baghdad, Baqouba, Mosul, Ramadi and Mahaweel. U.S. troops and insurgents traded heavy fire on the outskirts of Fallujah.
In other developments:
The heaviest fighting was in Baqouba, northeast of the capital, where guerrillas shot their way into a government office complex, seized two police stations and destroyed the home of the provincial police chief. Insurgents brandishing automatic weapons and rocket-propelled grenades roamed streets deserted by police.
In several hours of fighting, U.S. tanks rolled into the city, machine guns blazing, and aircraft dropped three 500-pound bombs on insurgent positions near the soccer stadium, Maj. Neal O'Brien said. By afternoon, control of the buildings was restored.
Two American soldiers died in the Baqouba fighting, the 1st Infantry Division said.
But the day's worst bloodshed came in Mosul — the country's northern metropolis often touted as a success story in restoring order in Iraq — where the U.S. military said 62 people were killed, including a U.S. soldier, and more than 220 people were wounded.
Most died when at least four car bombs rocked the police academy, two police stations and the al-Jumhuri hospital.
U.S. troops recaptured the Sheik Fathi police station in a hail of gunfire, and Iraqi troops raided a nearby mosque used by insurgents, the U.S. military said. Mosul's governor imposed an overnight curfew.
In Ramadi, an insurgent stronghold 60 miles west of Baghdad, gunmen barraged a police station with rocket-propelled grenades, destroying the building. At least 20 people were killed in the city, according to the Health Ministry.
"We were inside the station and suddenly there was a very heavy explosion," police 1st Lt. Ahmed Sami said. "We discovered later on that the station was attacked from all around."
Coalition officials said the offensive could augur escalated attacks in Baghdad in coming days.
Al-Zarqawi's followers claimed responsibility for Thursday's attacks in a statement posted on an Islamic Web site often used by his Tawhid and Jihad movement. The statement said the "occupation troops and apostates" — meaning Iraqi police — "were overwhelmed with shock and confusion."
Al-Zarqawi earlier claimed responsibility for the kidnappings and beheadings of American businessman and South Korean hostage , and an audiotape released Wednesday purporting to be by al-Zarqawi threatened to kill Iraq's prime minister.
Analysis of the tape showed it likely was al-Zarqawi's voice, a CIA official said Thursday.
American and Iraqi officials insisted the transfer of power would proceed as planned June 30. On Thursday, the coalition turned over the last 11 government ministries to Iraqi officials.
During the handover ceremony, interim Prime Minister Iyad Allawi said the attacks were "only acts of disturbances conducted by cowards" meant "to foil the democratic process."
The assault showed continued weakness among the security forces Allawi has vowed to reinforce to fight insurgents.
Motorists who drove through Fallujah said insurgents and uniformed Iraqi police appeared to be cooperating, chatting amiably on the street corners.
Only four days ago, the U.S. Army handed over security duties in the Baqouba suburb of Buhriz after hammering insurgents there in heavy fighting. U.S. military officers said then that they were confident the Iraqis could control the security situation.
But on Thursday, U.S. helicopter gunships swooped low over Baqouba, firing at suspected guerrilla hideouts in palm groves. Some motorists flew white flags from their car antennas, trying to avoid being hit.
Harried doctors, some working in bloodstained white coats, struggled to cope with a stream of wounded brought to Baqouba's hospital in civilian cars and pickup trucks. Corridors in the emergency room were spattered with blood. The Health Ministry said 13 people were killed and 15 wounded.
The wounded screamed in agony, and many of their friends and relatives directed their anger at the Americans, whom they blamed for destroying the order imposed by Saddam Hussein.
"May God destroy America and all those who cooperate with it!" one man screamed in the corridor. Another carried the body of a young man shot in the back of the head. "Oh God! Abbas is dead!" he cried.
In the Rasheed area of Baghdad, someone dressed in an Iraqi police uniform carrying a suitcase or a briefcase blew himself up near a U.S.-Iraqi checkpoint, killing four Iraqi soldiers and wounding at least one American, U.S. soldiers said.
Insurgents also attacked four Baghdad police stations with mortars, hand grenades and Kalashnikov rifles, but the U.S. military said Iraqi police fended off the attackers.
In Mahaweel, south of Baghdad, a bomb exploded outside the police station, killing one officer and wounding six.