BAGHDAD  Insurgents struck at the heart of the Iraqi government on Wednesday in two huge and deadly bombings that exposed a new vulnerability after Americans ceded control for security here on June 30. Nearby American soldiers stood by helplessly  despite the needs of hundreds of wounded lying among the dead  waiting for a request for assistance from Iraqi officials that apparently never came.

“As much as we want to come, we have to wait to be asked now,” said an American officer who arrived at one site almost three hours after the blast and who spoke on the condition of anonymity because he was not authorized to brief reporters. At one blast site, American soldiers snapped pictures of the devastation before ducking out of the streets.

After weeks of escalating violence in Iraq, the powerful truck bombs on Wednesday killed at least 95 people and wounded nearly 600 at and around the Foreign and Finance Ministries in central Baghdad, assaults on symbols of government that lent an air of siege to the capital. The bombs crippled the downtown area, closed highways and two main bridges over the Tigris River, and clogged hospitals with the wounded.

The bombings, the worst since American forces handed over security responsibilities for cities to Iraq at the end of June, shook the Iraqi government’s confidence that it was ready and able to secure the nation.

Prime Minister Nuri Kamal al-Maliki called for a reassessment of his security measures, calling the attacks “a vengeful response” to his recent, optimistic order to remove blast walls from the streets of Baghdad.

A Defense Ministry spokesman, Maj. Gen. Mohammad al-Askari, was quoted by Reuters as telling American and Iraqi military officers: “We must face the facts. We must admit our mistakes, just as we celebrate our victories.”

And Baghdad’s security spokesman, Maj. Gen. Qassim al-Moussawi, told the state-owned television station Iraqiya, according to Reuters, that attacks were “a security breach for which Iraqi forces must take most of the blame.” He said a number of security force officials were detained pending an investigation.

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A senior Shiite politician went on Iraqiya to call on Mr. Maliki to fire the security and intelligence officials responsible for the areas that were attacked.

“We must punish those who made mistakes,” said the politician, Hadi al-Ameri.

The explosions, one close to the heavily fortified Green Zone and the other less than three miles away, sent plumes of smoke billowing over the capital, ripped a gaping hole in a compound wall and set cars ablaze, trapping drivers inside.

“The whole thing is just so disgusting,” the United States ambassador, Christopher R. Hill, said as he read reports from his staff about the extent of the damage while on an official visit to the northern city of Kirkuk. “They’re just psychopathic.”

Around 11 a.m., the two truck bombs struck the Finance Ministry and the Foreign Ministry within three minutes, officials said, sending heavy smoke into the sky. The first blast, near the Finance Ministry, killed at least 35 people, collapsed a main elevated highway nearby and left rubble littered with shrapnel and blood. The second, more powerful blast near the Foreign Ministry killed at least 60 people, shattered windows inside the Green Zone and shook houses throughout Baghdad.

At roughly the same time, attacks in other parts of the city, including three roadside bombings and some mortar and rocket fire, left 17 people wounded, Iraqi officials said.

Though no one claimed responsibility for the attacks, Iraqis doled out blame both to their government and to the United States for coming to Iraq in the first place.

“This country is finished,” said one resident, Jamil Jaber, 45, whose five-room home behind the Foreign Ministry had been flattened, crushing his 4-month-old grandson. “It’s just robbery and killing.” He cursed the United States and former President George W. Bush.

Since the beginning of July, bombings in northern Iraq  for which officials blamed Al Qaeda in Mesopotamia and an affiliate, the Islamic State of Iraq have killed at least 140 people. The attacks on Wednesday might have been a signal from these groups that they could also assault the capital.