Nigerian President Goodluck Jonathan visited on Saturday the site of a bomb attack at the U.N. building in Abuja, refusing to be drawn on who was to blame but recognising the threat posed by a radical Islamist sect.
Authorities put the death toll at 19 in Friday's attack, when a car slammed through security gates of the United Nations offices in the capital, crashed into the basement and exploded, sending vehicles flying and setting the building on fire.
"I and all Nigerians are shocked," Jonathan told reporters and emergency workers at the charred U.N. building. "We will work with the U.N. and other world leaders to ensure that terrorism is brought under control."
So far there has been no confirmed claim of responsibility for the attack in which the car's driver was killed, possibly making the incident Nigeria's first suicide bombing.
However, analysts, security forces and diplomats said the attack had all the hallmarks of Boko Haram, a radical Nigerian Islamist group whose name roughly translates as "Western education is forbidden".
Asked by a reporter whether he thought Boko Haram was responsible, Jonathan gave no direct answer but acknowledged that the sect posed a serious threat. "Boko Haram as a local group is linked with terrorist activities and as a government we are working to bring it under control," he said.
Jonathan has been wary of assigning responsibility for bomb attacks since he quickly cleared a militant group from his home Niger Delta region of involvement in an October 2010 blast, only to back away when it was found the group had been involved.
Boko Haram, which mostly operates in the remote dusty northeast near the borders of Cameroon, Chad and Niger, wants sharia law more widely applied across Nigeria and has killed more than 150 people in bombings and shootings this year.
Jonathan imposed a security clampdown following the attack and armed soldiers patrolled Abuja, searching cars at roadblocks across the city, which sits in the centre of the country where the mostly-Christian south and largely-Muslim north meet.
The BBC said Boko Haram had contacted it to take responsibility for the attack. However, such claims are hard to verify because the sect has an ill-defined command structure and many people say they speak on its behalf. The police and government have yet to say who was behind the attack.
Intelligence officials say they have evidence that some Boko Haram members have trained in Niger and have connections with al Qaeda's North African wing, Al Qaeda in the Islamic Maghreb.
One security source suggested a link with simmering opposition to Jonathan in northern Nigeria, where Boko Haram is based.
Jonathan, a Christian southerner, comfortably won a presidential election in April that international observers and many Nigerians said was the fairest in decades.
But he infuriated some northern members of his own party who believed it was a northerner's turn to run for president, under an unwritten rule that rotates the presidential candidate for Nigeria's main political party between the north and south.
The security source noted that Boko Haram had so far attacked local rather than international targets. "This raises the international stakes and looks like the work of Boko Haram or a similar organised branch," he said, requesting anonymity.
However, he raised the possibility of "a northern political dimension", noting that some of Jonathan's enemies in the north "did say they would make the country ungovernable if he won the election".
During the election, a small section of supporters of Jonathan's opponents said they would carry out widespread attacks if he won. His opponents publicly condemned the threats.
Diplomats and security experts say Boko Haram is multi-layered. While it has a hardline core, some attacks have been carried out by disillusioned youths who feel let down by the state and are easily coerced by politicians, they say.
The north has much higher illiteracy, poverty and unemployment rates than the south.
Boko Haram has said it was behind almost daily attacks in the remote northeast, and a car bombing at police headquarters in Abuja in June.
U.N. Secretary General Ban Ki-moon has sent his deputy Asha-Rose Migiro to meet officials in Abuja. Nigerian presidency sources said they expected Migiro and U.N. security chief Gregory Starr to arrive in Abuja later on Saturday or early Sunday.