Afghan Interior Ministry police and U.S. soldiers quickly blocked off the area to prevent crowds of curious onlookers from gathering. Witnesses said they saw the wreckage of a large delivery van that might have been used by the bomber, as well as six vehicles of the type used by U.S. contractors.
RFE/RL correspondents in Kabul spoke to witnesses at the scene. One Afghan man, who would not give his name, described what he saw just minutes after the blast.
"When I reached the site of the explosion, I saw a few American soldiers who had their backs up against a tree," he said. "They were scanning the area with their guns raised. They were securing the area, and when I looked toward the place where the explosion happened, there was fire from a burning car. The car was overturned, and the place was very crowded."
Kabul resident Ahkbar Shinwari heard the explosion while saying evening prayers at home. Shinwari said he rushed to the scene and saw the bodies of the dead and injured scattered on the street, while a large fire raged within the DynCorp building.
"I was praying at that time, so I know that it was at 17:45 (Kabul time) that I heard the sound of the blast. It was a very, very heavy explosion," Shinwari said.
General Baba Jan, the Afghan Interior Ministry's security commander for Kabul, told RFE/RL that an explosives-laden vehicle managed to slip through security checkpoints at both ends of the street and stop directly in front of the DynCorp office. That office is just a few hundred meters from a residential building used by United Nations staff.
Interior Ministry sources later said an Afghan man suspected of being the driver has been detained for questioning.
"In this area, there were two houses of our international friends," General Baba Jan said. "This was not a military center, and this explosion was not caused by a suicide attack. It was a car bomb."
DynCorp officials have not yet commented on the bombing.
The Kabul attack came just hours after an explosion late on 28 August killed at least nine people -- eight of them children -- at a religious school in the country's southeastern Paktiya Province near the town of Zormat. No one has claimed responsibility for that blast.
The school is in an area directly across the border from Pakistan's autonomous tribal regions, where Pakistan's military has been waging a campaign against Al-Qaeda fighters and Islamic militants.
Western diplomats in the past week have accused Islamabad of turning a blind eye to Taliban fighters who are sheltering in Pakistan and crossing into Afghanistan to carry out terrorist attacks. The diplomats also have warned about intelligence reports suggesting Taliban fighters based in Pakistan are planning major attacks near the border and in Kabul.
Paktiya Province Governor Asadullah Wafa told AP that the school explosion was the work of what he called "puppets listening to their bosses outside the country." That term has been used by Afghan officials in the past to describe Taliban fighters in Pakistan.
Pakistan's security forces have repeatedly denied any knowledge of Taliban fighters on their territory, saying most of the hard-line members of the Taliban remain in Afghanistan.
Barnett Rubin of New York University is one of the United States' top experts on the region. He told RFE/RL just before the two blasts that elements in Pakistan's security services appear to be letting the Taliban survive inside Pakistan so that Islamabad can use them for future leverage against the government in Kabul.
"The Pakistani military is moving against Al-Qaeda, [but] they're not doing anything against the Taliban," Rubin said. "Pakistan has no credibility. They've been supplied with information about the exact location of various major Taliban leaders. And they have done nothing. Instead, whenever there is pressure on [Pakistan] about the Taliban, they arrest more Al-Qaeda people -- meaning people from Arab countries or from small extremist groups. But they do not move against the Taliban."
The U.S. Embassy in Kabul also has been warning its citizens in Afghanistan about possible bomb attacks against Western targets. Today, the embassy issued a fresh warning to Americans in the Afghan capital, telling them to avoid potential target areas, such as government offices, NATO bases, and restaurants.
(RFE/RL's Afghan Service contributed to this report.)