A series of powerful explosions reverberated across the heart of Baghdad today, killing 95 people and wounding 536 on the deadliest day in the capital since U.S. forces completed their withdrawal from Iraq's cities June 30.

The main targets were the Finance and Foreign ministries, which were shaken by massive explosions minutes apart, demonstrating that the insurgency still has the capacity to strike at will against major institutions.

In the first attack, a car bomb demolished a bridge beside the Finance Ministry.

Fifteen minutes later, a truck bombing on the edge of the fortified Green Zone outside the Foreign Ministry rattled windows across the city and killed dozens of people.

The bombing ignited several cars and left a crater in the road outside the ministry, where scores of employees were injured by flying glass, a witness said. Windows were shattered at the nearby Rashid Hotel, home to many politicians, and at the parliament building across the street.

It appeared that most of the casualties were from the second explosion, but police said they did not have an accurate breakdown.

About the same time, two mortar shells or rockets landed in a busy central Baghdad market area, damaging one of the bridges spanning the Tigris River and killing at least six people. Fifteen minutes later, two smaller explosions in a west Baghdad neighborhood killed two people.

Officials said that the toll could rise as bodies are counted, and that one major hospital had closed its doors to casualties because it was swamped. Streets were sealed off across the city, bringing life in many areas to a standstill.

Gaith Abdullah, 38, who owns a fabric store in the market area, described scenes of panic and mayhem as the explosions rippled across the capital.

After hearing the first blast at the Finance Ministry, he decided to close his shop. As he headed home, two mortar shells struck the road ahead of him.

"I saw people killed and wounded on the ground and many cars were ablaze," he said. "The security forces started shooting and were firing randomly. Then another massive explosion shook the whole place," apparently the blast at the Foreign Ministry.

The bombings came at a time when the insurgency appears to be making a concerted effort to undermine faith in the ability of the Iraqi army and police to sustain security.

Prime Minister Nouri Maliki has trumpeted the relative calm that has prevailed in Baghdad since U.S. forces pulled out as evidence that the Iraqi forces are capable of providing security.