Sharia law: a recurring violence trigger in Nigeria
Clashes between security forces and radical Islamists which claimed at least 65 lives since Sunday are a grim reminder that religion remains an explosive issue since the 2000 introduction of Sharia law in 12 of Nigeria's's 36 states.
If the bloody unrest in the oil-rich Niger Delta of the past three years appear to be based on economic demands, repeated religious riots in the north represent a deep-rooted tendency with serious consequences for the unity of the Nigerian federation.
Nigeria's 140 million population are roughly evenly divided between Muslims, mainly in the north, and Christians, in the south.
Ex-president Olusegun Obasanjo, a Christian, in power between 1999 and 2007, had recalled in February that the introduction of the strict Islamic code (Sharia) in the north was "the greatest challenge" of his regime.
The nation has in the past decade been visited by regular bouts of ethnic-religious riots which have claimed thousands of lives, while some churches and mosques were torched.
The latest bloody clashes were in November last year when more than 700 people died in the central city of Jos, according to Human Rights Watch (HRW), the New York-based non-governmental organisation.
Officials put the death toll at 220.
Troops were called in to intervene in the clashes between Muslims and Christians in which machetes were freely used.
In northern Nigeria, Islam dominates in all aspects of life: Islamic courts, Islamic police oversee "good manners" such as wearing of decent clothes by students in certain states, strict censorship of films produced locally in what is dubbed Kannywood.
Police also see to the separation of the sexes in public places, not to mention the ban on alcohol consumption and homosexuality.
Women are treated as second class citizens.
The socio-political pressure is very strong and constitutes, according to analysts who spoke to AFP, a major handicap to modernisation, economic and cultural development.
A typical dramatic example was the refusal, in 2003, of Muslim leaders in the region to support a UN-inspired anti-polio drive, denouncing it as a "plot" by the United States to sterilise Muslims.
The programme was then halted for 13 months.
President Umaru Yar'Adua, was before his ascension into office the state governor of Katsina State when in 2002 a young woman, Amina Lawal, 31, was condemned to death by flogging by a Sharia court for adultery.
Despite international pressure, he failed to impose his authority on the court which convicted her.
She was finally acquitted the following year by an Islamic appeals court in the same state.
In the general context of profound poverty, Islam in the northern Nigeria is not aggressive, but economic pressure and the absence of hope for development create fertile ground for radical movements such as the "Taliban," which struck in Bauchi and three other states.
In 2001, when the United States launched a crackdown on the Taliban regime in Afghanistan, Niger shut its borders against Nigeria, its southern neighbour, the origin of T-shirts with the picture of Osama bin Laden that began to flood markets in the towns of Maradi and Zinder.