LAGOS A Nigerian man linked to al Qaeda tried to set off an explosive device aboard a U.S. passenger plane as it approached Detroit on Friday, but was overpowered by passengers and crew, officials said.
Following are questions and answers about Islam in West Africa and radical groups which have tried to gain a foothold.
DOES RADICAL ISLAM HAVE A FOOTHOLD IN WEST AFRICA?
Nigeria is Africa's most populous nation, roughly equally divided between Christians and Muslims spread across more than 200 ethnic groups who generally live peacefully side by side.
West Africa has a strong tradition of moderate Sufi Islam whose brotherhoods are renowned for their tolerance, particularly in the Sahel, the southern fringe of the Sahara desert stretching across the northern edge of Nigeria.
Salafist insurgents from Algeria, Tablighi clerics from Pakistan and Wahhabist missionaries from Saudi Arabia -- all seen as potential threats by Western intelligence services -- have tried to gain a foothold in West Africa in recent years.
By and large they have failed, with their ideologies rejected by the vast majority of West African Muslims.
IS AL QAEDA ACTIVE IN NIGERIA?
The main militant threat in the Sahara is seen as al Qaeda's North African wing, al Qaeda in the Islamic Maghreb, which grew out of Algeria's civil war in the 1990s and was formerly known as the Salafist Group for Preaching and Combat (GSPC).
U.S. military officials have said in the past said the group is active in Mali and used Mauritania and Niger, on Nigeria's northern border, to host mobile training camps, often believed to be little more than a few jeeps around a watering hole where recruits learn to use satellite phones and explosives.
Nigeria arrested a group of Islamists with suspected links to al Qaeda in 2007 and some Western diplomats have expressed concern that -- with its huge population, widespread poverty and strategic importance as an oil supplier to the West and to China -- it could become a target for radical Islamic groups.
But there has been no conclusive evidence of an al Qaeda presence in Nigeria.
ARE THERE RELIGIOUS TENSIONS IN NIGERIA?
Clashes between security forces and a radical Islamic sect called Boko Haram -- which wanted a wider adoption of sharia (Islamic law) -- killed hundreds of people in the northern Nigerian city of Maiduguri in July.
The group is sometimes referred to as the "Nigerian Taliban" but its chaotic tactics have little in common with those of Islamic militant groups elsewhere and no conclusive evidence of links to the Taliban in Afghanistan have been made public.
Islamic jurisprudence in Nigeria is based on the moderate Maliki school of Sunni Islam and Boko Haram's ideology is widely dismissed by the country's Muslim leaders and believers.
The stricter enforcement of sharia in 12 of Nigeria's 36 states in 2000 alienated sizeable Christian minorities in the north and sparked clashes which killed thousands.
In 2002 at least 215 people died in rioting in the northern city of Kaduna following a newspaper article suggesting the Prophet Mohammad would probably have married one of the beauty queens at a Miss World contest being held in the capital Abuja.
A Muslim protest against Danish cartoons of the Prophet Mohammad in Maiduguri ran out of control in 2006, sparking a week of rioting which killed at least 157.
(Editing by Myra MacDonald)