A bomb blast at a bus station in the Nigerian capital, Abuja, killed at least 71 people and wounded 124 as commuters gathered for the Monday morning rush hour.
Suspicion immediately fell on Boko Haram, Nigeria's main armed group, which has been threatening to attack the capital.
Boko Haram has as its main aim the establishment of a separate Islamic state in the country's northeast and has killed nearly 1,500 people this year. Nigeria, Africa's most populous nation, has a population of about 170 million, divided almost equally between Muslims mainly in the north and Christians in the south.
The group's violent campaign is seen to pose the greatest threat to the cohesion and security of the central Nigerian government ahead of elections in February 2015.
Monday's blast ripped a large hole in the ground of Nyanya Motor Park, about 10 miles from the city center, and destroyed more than 30 vehicles, causing secondary explosions as their fuel tanks ignited.
"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.
Security personnel cordoned off the area, and a bomb detonation team was combing it for secondary explosives, which are common in attacks in Nigeria.
The blast appeared to come from a vehicle at about 6:45 a.m., according to Nigeria's National Emergency Management Agency. "It affected quite a number of people because it was still very early in the morning and there was a lot of traffic," according to the agency's Air Commodore Charles Otegbade. He did not give a death toll. But emergency services later confirmed to Al Jazeera that at least 71 people were killed.
No group has claimed responsibility for the attack, though bus stations are a favored Boko Haram target.
Boko Haram claimed responsibility for a 2011 suicide bombing by two explosives-laden cars that drove into the lobby of the United Nations office building in Abuja. It killed at least 21 people and wounded 60.
Last week, Boko Haram suspects detained at the State Security Service headquarters in Abuja, next door to the residence and office of President Goodluck Jonathan, staged a failed jailbreak in which it is suspected that they had outside help. The agency said 21 detainees were shot and killed and two agents wounded in a shootout that lasted more than two hours.
The militants are blamed for attacks in northeastern Nigeria that have killed more than 60 people in the past five days, including eight teachers living at a boarding school that had been closed because of frequent attacks on schools, in which hundreds of students have died.
Boko Haram — which in English means "Western education is forbidden" — has been attacking schools, villages, marketplaces and military barracks and checkpoints this year in increasingly frequent and deadly attacks.
The military has claimed that it has the extremists on the run with almost daily air bombardments and ground assaults on hideouts in forests and mountain caves along the border with Cameroon. But the government has come under international scrutiny for alleged human rights violations in its ongoing crackdown on the group.
Al Jazeera and wire services