Nigeria's intelligence agency said it has been warning shopping complexes in Abuja for two weeks that Islamic extremists might attack them in the capital, where a blast at a mall killed 22 people this week.
The increased security may have prevented even more carnage as witnesses said a security guard stopped a car bomber from entering the mall moments before the massive explosion on Wednesday.
Survivor Donald Chikason told ThisDay newspaper that a security guard argued with the driver of a car who wanted to enter Emab Plaza through the exit gate. When the guard refused, the man bent down and moments later the car exploded, Friday's edition of the newspaper quoted him as saying.
"The man started arguing, behaving as if he was drunk," it quoted him as saying.
Chikason, who works at a bank in the mall, was knocked unconscious by the blast and regained consciousness in the hospital.
The explosion was heard miles (kilometers) away. It set 17 vehicles ablaze and shattered windows throughout the four-story complex.
Body parts lay around the exit gate, other witnesses told The Associated Press. Dozens of wounded survivors were recovering in the hospitals Friday, most suffering burn wounds like Chikason, but at least one victim's leg was amputated, doctors said.
Nigerian intelligence received information that Boko Haram extremists were planning such an attack, said spokeswoman Marilyn Ogar of the Department of State Security.
"About two weeks ago we heard information that they were planning an attack at a busy shopping mall or market ... and so we had to go from one shopping complex to another trying to tell people to be more aware," she told The Associated Press.
Emab Plaza is the biggest and busiest in Abuja, the nation's capital in central Nigeria. The explosion occurred around rush hour as many residents were hurrying to view Nigeria's Super Eagles match against Argentina at the World Cup in Brazil. It was unclear if the bomb was timed to coincide with that, although Boko Haram has bombed several football viewing venues this year, prompting two northeastern states to ban public events to watch the football spectacular.
The state security department did not publish the intelligence about the threat to shopping malls, apparently to avoid a panic. Last week the government warned it had information that Boko Haram planned to hijack petrol tankers in the capital and booby trap them with explosives.
Two separate bombs in Abuja in April killed about 120 people and wounded more than 200 at a busy bus station.
President Goodluck Jonathan returned home Thursday night, cutting short his participation at an African Union summit in Equatorial Guinea.
The capital is in mourning, with speedy burials for Muslims among the victims. They included artist Abba Kura. His friend, Muhammad Khalifa Garba wept at his funeral Thursday, where mourners carried his works. He said Kura told him earlier this week that he no longer wanted to paint on canvas and had started a new work, a landscape on paper.
A relative of another victim, Mohammed Maina Bissala, railed against Boko Haram's indiscriminate tactics: "Allah says you should not take the life of a single person, so why should you claim that you are Boko Haram and you are killing everybody, both Muslims and Christians, everybody. What have they done? They have not done anything, these are innocent souls," he told The Associated Press.
Boko Haram's attacks have been concentrated in its stronghold in the northeast of the country but it has spread its attacks to the capital this year and increased the tempo and deadliness of attacks concentrated around bombings in cities and a scorched-earth policy in rural villages in the northeast.
Boko Haram attracted international condemnation for the April mass abductions of more than 200
schoolgirls who remain captive, and is blamed for this week's kidnappings of another 90 people.
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