ABUJA (Reuters) - As long as violence perpetrated by Islamist militants was more or less contained in Nigeria's remote northeast, the attitude of many citizens and expatriates in the more prosperous south was a shrug of the shoulders.
But growing evidence that Boko Haram, or other violent groups or individuals inspired by it, are radiating attacks from their northeastern heartlands across Africa's most populous country has many Nigerians feeling that nowhere is safe.
Boko Haram leader Abubabar Shekau claimed responsibility for two blasts minutes apart targeting a fuel depot on June 25 in the country's main port in Apapa, in the commercial hub of Lagos, saying he had sent a bomber in do it.
The blasts were almost certainly caused by bombs, three senior security sources and the manager of a major container company told Reuters, and one was most likely the work of a female suicide bomber, although there are doubts about whether it was Boko Haram or another Islamist group inspired by them.
In Owerri, a city in the oil-producing Niger Delta, a botched bomb in a pentecostal church on June 15 before a Sunday service was due to start bore the hallmarks of Boko Haram, one of the security sources, who was investigating the blast, told Reuters. Christian worshippers have been a target of Boko Haram Islamists for several years, but this would be the first time the militants have struck the strategically vital oil region.
Police have said there is no proof that this was Boko Haram - the Delta has a history of political and criminal thuggery - but churches in this very Christian region were never attacked.
Add to these a string of bombings across the north, centre and in the capital of Africa's biggest economy and top oil producer, all of them well outside Boko Haram's main area of operations in Borno state, and a pattern emerges.
Some officials say Boko Haram, which made world headlines with the abduction of 200 schoolgirls in April, want to relieve pressure on itself in the northeast, where it has tried to carve out a de facto Islamic state.
Others say Boko Haram's ambitions never were confined just to the historical Islamic caliphates of the north.
"Not once has Boko Haram said it wants a caliphate just in the north. They see their constituency as Muslims everywhere," said Fatima Akilu, director of behavioural analysis in Nigeria's national counter-terrorism unit. "It's not a geographic caliphate with a boundary that ends in the north."
The charred, bloodied wreckage of a bomb blast outside Abuja's Ebam Plaza in the upmarket Wuse II district late last month has mostly been cleaned up, though the building's gate remains locked. Police said the final death toll was 24. Shekau claimed that one, too, in his video.
Boko Haram was seen as a "northern problem" until a bomber attacked Abuja's police headquarters in June 2011, killing several people in Nigeria's first recorded suicide attack.
Two months later a suicide truck bomb targeting the U.N. headquarters in Abuja killed 25 people.
But from mid-2012 the insurgents seemed to lose interest in staging attacks outside their core area of operations, preferring to consolidate their power base in the northeast.
A military offensive since May last year that was meant to dismantle their hold on the northeast changed that dynamic, prompting the insurgency to mutate in two ways: brutal attacks on civilians in the region dramatically surged, and efforts to strike out in areas far from the rebels' strongholds resumed.
As bombs spread across the country, there has also been a marked increase in deadly attacks blamed on Fulani cattle herders, especially easterly Benue and Taraba states, but which some officials suspect might be linked to Boko Haram.
Hundreds of settled farming peoples have been killed in night-time raids by heavily armed gangs in the past four months. Some of these attacks were so unusually brutal, in some cases including gunning down dozens of people as they fled and burning churches, they look more like the Islamists, the military says.
Defence Spokesman Major-General Chris Olukolade said in April that forces had engaged "a group of terrorists operating under the guise of herdsmen" in Taraba state. They arrested some.
Governor Gabriel Suswam of Benue state said attacks that killed more than 200 people there in March were being carried out by people with sophisticated weapons, not the homemade shotguns traditionally used by Fulani herders.
"The attacks are at night, the victims terrified. They don't know if they are Fulani or not," a military source told Reuters. "We think this is something else."
Boko Haram are mostly from the Kanuri ethnic group, it is unclear if some Fulani cattle keepers have been infiltrated.
A deadly attack on a bus park on the outskirts of Abuja in April, less than a month before Nigeria was due to host the World Economic Forum, and another two since, killed scores and left little doubt of a concerted effort to target the capital.
Police said on Saturday they had uncovered a plot to bomb the transport network, using suicide bombers and devices concealed in luggage at major bus stations.
Sometimes attacks have seemed calculated to stoke ethnic or sectarian conflict, such as one in May in the central city of Jos, a tinderbox of such tensions, that killed 118 people.
That one failed to ignite tit-for-tat reprisals. A similar effort in Lagos may be more successful, says Akindele. The even balance of power in Jos keeps revenge in check, but Lagos is overwhelmingly Yoruba. They would have less to fear from counter-reprisals if they took out their anger on northerners.
The target of the Lagos bombs was a fuel depot which, had it gone up, would have caused a massive chain explosion and disrupted Nigeria's mostly imported fuel supply. At least two people were killed. Police said it was an accident involving a gas canister, but the security sources say that was a cover-up - as did Shekau in his latest video.
If confirmed to be Boko Haram the ramifications are huge, both because Lagos is an international business hub and because it is a usually peaceful if at times uneasy melting pot of ethnicities from the mostly Christian south and Muslim north. Yorubas are split evenly between Muslims and Christians, but in past unrest with northerners, ethnic loyalties trumped religion.
"The Lagos government's very worried ... Lagos has a history of ethnic clashes, between (northern) Hausa and (southern Yoruba)," said Kayode Akindele, partner at Lagos-based consultancy 46 Parallels.
"There's a danger of that, if there's a serious loss of life. Lagos state also doesn't want to put off the investment world," he said.
Versions of exactly what happened at Apapa differ. One account is that a female suicide bomber blew herself up in a car, while another improvised device was thrown a few minutes earlier. Both were near fuel tankers at a depot.
But security sources say a more credible version was that the first bomb was a car bomb - photos of a mangled chassis have circulated in some local press - while the suicide bomber was on foot. Unverified pictures of her severed head, usually evidence of a suicide vest, have also circulated.
"The suicide bomber is much less certain because it's focused on eyewitness accounts. We don't have any permanent evidence," said Thomas Hansen of Control Risks consultancy.
The amateur nature of the apparent suicide attack - she blew up a few 100 metres before anywhere that could have done damage, though no one intercepted her - suggests she hadn't had expert training, one security source says, but Boko Haram would still want to claim it to spread fear.
"Our impression is ... a local faction inspired by Boko Haram that has attempted to target the fuel supply chain, not operating under direct command and control," said Hansen. "In terms of planning, it appears not to have been as sophisticated as some attacks elsewhere in Nigeria."
(Editing by Will Waterman)