Survivors screamed in anguish and the stench of burning fuel and flesh hung over the area, where billows of black smoke rose as firefighters worked to put out the fires. Rescue workers and police gathered body parts as ambulances rushed the wounded to hospitals.
Visiting the blast scene, President Goodluck Jonathan blamed Boko Haram, the homegrown terrorist network that has targeted schools, churches, mosques, villages and government facilities, killing thousands in its five-year campaign to make Nigeria an Islamic state.
Authorities said at least 72 people were killed and 164 wounded, though the death toll was sure to climb because it did not include victims whose bodies were dismembered, the health ministry said. It was the deadliest attack yet in Abuja, the centrally located capital that is hundreds of miles from Boko Haram's stronghold in Nigeria's northeast.
"I can't count the number of people that died. They took them in open vehicles. People were running and there was confusion," said civil servant Ben Nwachukwu.
A counter-terrorism expert said the bomb appeared to have been buried underground, while the emergency management agency said the explosives were apparently hidden in a vehicle.
Bus driver Tunji Adeniran said he was about to leave the bus terminal when the explosion struck. "The bomb shattered my vehicle," he said. "One vehicle was in front of me. As he started his car, I heard a loud noise. I thought it was his car that exploded."
Adeniran said his brother, bank worker Mohammed Ochai, was fatally injured in the blast and died on the way to the hospital.
The explosion, which struck at 6:45 a.m. in the poor satellite neighborhood of Nyanya, left a 4-foot-deep crater and destroyed 16 luxury buses and 24 minibuses and cars, police spokesman Frank Mba said.
Security personnel battled to cordon off the area as a bomb detonation team combed it for secondary explosives amid fiery blasts from exploding car tanks ignited by the blaze. Thousands of bystanders gathered, ignoring warnings to stay away.
While Jonathan blamed Boko Haram, there was no immediate claim of responsibility for the bombing, though bus stations are a favored Boko Haram target. In March 2013, the extremists drove a car bomb into the main bus station in Kano, Nigeria's second-biggest city, killing at least 25 people.
Touring the blast site Monday, Jonathan tried to downplay the terrorist network's reach, saying, "the issue of Boko Haram is temporary. Surely, we will get over it."
In Washington, U.S. State Department spokeswoman Jen Psaki said the Obama administration was "outraged by these senseless acts of violence against innocent civilians."
"We encourage the government of Nigeria to conduct a full investigation to identify and bring justice to the perpetrators of these attacks. We continue to stand with the Nigerian government and people as they grapple with violent extremism."
Interpol secretary general Ronald K. Noble offered to deploy a special response team to help investigate what he deplored as "this mass murder."
Boko Haram's campaign to make Nigeria an Islamic state poses the greatest threat to its cohesion and security and imperils nearby countries where its fighters have gone to train. Fighters from Chad, Cameroon and Niger have been found among extremists in Nigeria, whose 170 million people are divided almost equally between Muslims living mainly in the north and Christians in the south.
While the capital of Africa's most populous country had remained relatively peaceful even as Boko Haram attacks in northeast Nigeria have increased, there have been notable exceptions, including a 2011 car bombing of the local U.N. headquarters that killed 21 people and wounded 60.
In May 2013, Jonathan declared a state of emergency and deployed thousands of troops to the northeast after the extremists took control of entire towns and villages. Security forces quickly forced the insurgents out of urban areas but have been battling to dislodge them from hideouts, despite near-daily air bombardments and ground assaults this year on forests and mountain caves along the border with Cameroon.
The military has claimed it has the upper hand in the war against the Islamic militants, but governors in the northeast contend Boko Haram is better armed and motivated.
Governors and traditional leaders in the northeast have demanded that Jonathan end the state of emergency, saying it is causing suffering and has not been effective. Some 750,000 people have been forced from towns and villages, including tens of thousands of farmers, risking a food shortage.
Monday's attack likely will give Jonathan a boost in the short term, the Washington-based Eurasia Group political risk consultancy said. "Parliament is now likely to approve the administration's request to extend the state of emergency. ... The attack may actually bolster the administration's political fortunes," said the group's Africa director, Philippe de Pontet.
The deadliest toll in the uprising came March 14 when Boko Haram attacked the main military barracks in the northeast, Giwa Barracks in Maiduguri, and freed hundreds of detainees. Amnesty International said more than 600 people were killed, most of them unarmed detainees gunned down by soldiers.
Last week, Boko Haram suspects detained at the State Security Service headquarters in Abuja, next door to the presidential villa, staged a failed jailbreak in which it is suspected that they had outside help. The agency said 21 detainees were killed and two agents wounded in a shootout that lasted more than two hours.
In a warning emailed to U.S. citizens after Monday's blast, the U.S. State Department urged avoiding locations where large crowds gather such as churches, mosques and markets, as well as hotels and malls frequented by foreigners.