LAGOS (Reuters) - Christmas Day bomb attacks against churches in Nigeria by Islamist militant group Boko Haram targeted the country's religious and ethnic faultlines in an apparently escalating campaign to fracture the nation's stability.
The shadowy group from Nigeria's Muslim north, blamed for dozens of bombings and shootings in recent years, said it was responsible for a string of blasts, three of them in churches, including one that killed at least 27 people at a packed Christmas service on the outskirts of the capital Abuja.
The attacks, days after clashes between security forces and Boko Haram militants killed at least 68 people, show evidence of increasing coordination and strategy by the group that ought to ring alarm bells in Nigeria and Western capitals.
The attacks strike at historic internal religious and regional divides that have often threatened the integrity of Africa's most populous state since its independence from Britain in 1960 - dangerous divisions that included a brief but bloody civil war over the secession of Biafra in the eastern region.
The Christmas church bombings included one in the central city of Jos, a religious and ethnic flashpoint region lying in the heart of the divide between the mercantile, largely Muslim pastoralist peoples of the north and the traditionally farming, largely Christian peoples of the south.
Nigeria's 160 million people are split roughly evenly between Christians and Muslims, who for the most part live side by side in peace, but their cohabitation in the "Middle Belt" has sometimes been a source of tensions over land and influence.
Jos in particular has seen many hundreds killed in periodic outbreaks of vicious ethnic and sectarian violence.
The attacks on the churches on one of global Christianity's most important feast days appeared aimed at touching off this latent tinderbox, just as targeted sectarian attacks in Iraq have tried to provoke Sunni-Shi'ite strife.
In December last year, Boko Haram also claimed responsibility for Christmas Eve bombings around Jos and attacks on churches and clashes that resulted in more than 80 deaths.
The latest attacks dramatically increase the challenge facing the government of President Goodluck Jonathan.
He is a Christian southerner. Critics have accused him of trying to deal with Boko Haram purely as a security question, instead of doing more to tackle issues of poverty, youth unemployment, corruption and perceived alienation and resentment among Muslim northerners.
His response to the attacks on Sunday - describing them as "unfortunate" and telling Nigerians Boko Haram would "not be (around) for ever, it will end one day" - could be seen by many as complacent.
The militant movement, whose name means "Western learning is sinful" in the northern Hausa language, is concentrated in Nigeria's more remote northern states. It became active in 2003, with an avowed aim to introduce sharia law across Nigeria.
The latest attacks will fuel the fears of Nigerian and Western security experts who increasingly link Boko Haram to a wider violent militant Islamic jihadist threat from North Africa across the Sahara.
They could also invite more Western counter-terrorism support for Nigeria and fellow governments in West Africa's strategic oil-producing Gulf of Guinea region - a growing energy supplier to the United States and other Western powers seeking to temper their over-reliance on the Middle East.
The head of the U.S. military's Africa Command, General Carter Ham, lists Boko Haram along with al Qaeda in the Islamic Maghreb and Somalia-centred al Shabaab as groups violently hostile to U.S. and Western interests who have increasingly begun to cooperate among each other..
Nigeria's military sees even closer links with al Qaeda..
Such analysis points to the increasing sophistication and organization of the Boko Haram attacks, moving from disparate shootings and bombings to more coordinated headline-grabbing actions, seeking national and international impact.
The Christmas Day bombings are the group's most high-profile strike since a suicide bombing - Nigeria's first - that hit United Nations headquarters in Abuja in August, killing at least 23 people.
But experts warn that tackling Boko Haram as a security problem alone will not address the underlying social, economic and political problems that underpin the group and its domestic support, and that a heavy-handed police and army response could simply exacerbate the threat being incubated in Nigeria's north.
John Campbell, a former U.S. ambassador to Nigeria, says Boko Haram has given voice to what he calls "a cloud of inchoate rage shaped by Islam" that has brewed among northerners.
"(President) Jonathan needs to address this northern alienation, of which Boko Haram is only a symptom," Campbell wrote in a recent op-ed for Foreign Affairs magazine.
"Too heavy a hand would risk alienating Nigeria's 75 million Muslims, who already have legitimate grievances in the north. This, in turn, could undermine the very unity of Nigeria - something neither Washington nor Abuja can afford," said Campbell, who is the Ralph Bunche senior fellow for Africa policy studies at the Council on Foreign Relations in New York.
Writing by Pascal Fletcher