BAGHDAD, Iraq – Guerrillas bombed a Baghdad shopping street full of police recruits and fired on a police van north of the capital yesterday in attacks that killed at least 59 people and struck at the heart of the American strategy for fighting the escalating insurgency.

The car bombing and shooting – the latest in violence that has killed nearly 150 people in three days – were part of an increasingly brazen and coordinated campaign to bring the battle to Baghdad, sowing chaos in the center of authority for the prime minister, Ayad Allawi, and his American allies.

Insurgents appear to have only grown deadlier since Mr. Allawi’s interim government took power in June, despite American claims that Iraqi security forces are showing more resolve against insurgents.

The mounting attacks aim to wreck the centerpiece of the American plan for defeating the militants: Building a strong Iraqi security force able to bring some calm before elections slated for January. Doing so is also a key prerequisite for any withdrawal of American troops.

The Tawhid and Jihad group, headed by Jordanian militant Abu Musab al-Zarqawi, posted a Web statement claiming responsibility for yesterday’s car bombing. The Al Qaeda-linked group launched a surprise assault in Baghdad on Sunday, killing dozens, and boasted it had the upper hand in the fight against the Americans.

Last night, another loud explosion rocked Baghdad near the Green Zone, where Iraq’s interim government and the American Embassy are located. There was no immediate word on the cause.

The morning car bombing was the deadliest single attack in Baghdad in six months, wrecking buildings and cars on central Haifa Street, leaving charred bodies and hurling body parts, shoes, and debris into nearby trees and homes.

The blast ripped through stores where Iraqis were shopping and cafes where men applying for the police force were sipping tea and escaping the summer heat as they waited their turn to sign up at the nearby western Baghdad police headquarters.

The 47 dead included would-be police recruits and civilians. At least 114 people were wounded, said Health Ministry spokesman Saad Al-Amili.

In Baqouba, northeast of the capital, gunmen in two cars opened fire yesterday on a van carrying policemen, killing 11 officers and a civilian, said Qaisar Hamid of Baquba General Hospital.

Also yesterday, clashes between American troops and insurgents killed at least eight civilians and wounded 18 in Ramadi, a predominantly Sunni Muslim city west of the capital where anti-American sentiments are high.

The military said yesterday that three American soldiers were killed and eight wounded in separate attacks in Iraq in the past 24 hours.

Further highlighting the chaotic situation, electricity was knocked out across the country when saboteurs blew up an oil pipeline junction in northern Iraq, sparking a fire that set off a chain reaction in power generation systems.

In Cairo, the head of the Arab League warned that “the gates of hell are open in Iraq and the situation is getting more complicated and tense.” Amr Moussa appealed to Arab countries “to help Iraq to overcome this crisis.”

Despite the violence, American and Iraqi forces claimed two successes in recent days. American troops yesterday ended their siege of the northwest city of Tal Afar, saying they had cleared it of militants after 12 days of fighting that killed dozens of people.

Last Thursday, American troops entered Samarra, north of Baghdad, for the first time since May 30 after negotiating a deal with local leaders. The city had been a stronghold of Sunni insurgents.

American commanders insisted attacks like yesterday’s won’t deter Iraqis from joining the police and Iraqi national guard to help end the violence.

“I’m pretty sure that it’s not driving them away; it may in fact have the opposite reaction and strengthen their resolve to join the Iraqi forces,” said Lieutenant Colonel Steven Boylan, spokesman for coalition forces in Iraq. “They are tired of the killings and the bombings.”

Crowds at the scene of the Baghdad explosion pumped their fists in the air and directed their anger against America and Mr. Allawi for failing to protect the station even though police recruiting points have repeatedly been attacked.

“Bush is a dog,” they chanted.

“Such places were targeted before,” said Ali Abul-Amir, who had been waiting to join the police force. “I blame Ayad Allawi’s government for what happened because they did not take the necessary security measures.”

With medical teams overwhelmed, residents covered burned bodies with blankets and lay them on stretchers. Others collected severed hands, arms and legs and put them into cardboard boxes.

“Seconds earlier, people were drinking tea or eating sandwiches and then I could see their remains hanging from trees,” said Mahdi Mohammed, who was outside his barber shop when the explosion went off. “I could see burning people running in all directions.”

Some directed their anger at the insurgents.

“Such acts cannot be considered part of the resistance [against American forces.] This is not a jihad, they are not mujahedeen,” said Amir Abdel Hassan, a teacher. “Iraq is not a country, it’s a big graveyard,” he said.

With Mr. Allawi in power and January elections approaching, American commanders have said they are stepping up the training and arming of Iraq’s security forces.

The military has been training Iraqi police and the Iraqi Civil Defense Corps members for more than 18 months. But over the summer, the Army officer formerly in charge of training, Major General Paul Easton, acknowledged that misguided methods had wasted almost a year.

The forces’ weakness were highlighted in April, when police largely abandoned their stations in the face of an uprising by Shiite militiamen in Baghdad and southern cities. When the militia rose up again last month, U.S. forces did most of the fighting.

Iraqi police on duty numbered 31,300 in July, the last month for which figures are available. That is down from 90,803 in May. Some were sent for retraining, some were killed, and others were removed for supporting the insurgency.

Attacks on Iraqi security forces and police officers have killed hundreds of people in the 17 months since insurgents began their campaign to expel U.S.-led forces. From April 2003 to May 2004, 710 Iraqi police were killed out of a total force of 130,000 officers, authorities said.