By Felix Onuah and Camillus Eboh
ABUJA (Reuters) - Nigeria imposed a security clampdown on Abuja on Saturday, a day after a car bomb ripped through a U.N. complex in the capital, with authorities keeping an open mind on the perpetrators but suspicion focused on a local Islamist sect.
Armed soldiers patrolled Abuja's streets, searching cars at roadblocks across the city, which sits in the center of Africa's most populous nation where the mostly-Christian south and largely-Muslim north meet.
Authorities put the death toll at 19 following Friday's attack, when a car slammed through security gates of the United Nations office complex, crashed into the basement and exploded, sending vehicles flying and setting the building on fire.
"As of this morning we can confirm 19 dead. The final toll could be higher as some casualties are still in a bad condition," a spokesman for the Nigerian National Emergency Management Agency told Reuters.
"We have worked through the night helping the wounded, one of the biggest issues we've had is the pressure from people who have crowded hospitals and the bomb site searching for their friends and relatives," he added.
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."
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.
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.
Intelligence officials say they have evidence that some members have trained in Niger and have connections with al Qaeda's North African wing, Al Qaeda in the Islamic Maghreb.
However, one security source suggested a link with simmering opposition to President Goodluck 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 organized 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.
(Additional reporting and writing by Joe Brock; Editing by David Stamp)