Nigerian army attacks rebels in north

In response, President Umaru Yar'Adua sent in the army to the city of Maiduguri to shell the home of Mohammed Yusuf, the soft-spoken preacher who leads the Boko Haram sect -- known here as the Taliban. The army also attacked a mosque in the city.

Black smoke hung above Maiduguri, which throbbed with machine-gun and mortar fire, as the soldiers moved in. Gunfire continued overnight.

"It is too frightening to stay in my house," said Hamisu Balarabe, 38, a government employee who huddled at the station. "It felt like the mortars would land in my house. I have never heard such a terrifying sound."

"Al Qaeda's modus operandi is to look for local disputes which have a religious element and try to play on that and globalize the dispute. There's quite a dangerous potential for this to take on these sorts of global clash elements, but I don't think that's happening yet," Moncrieff said.

Sani Adamu, a journalist and security analyst in Bauchi state, said the militants were mostly illiterate school dropouts.

"The group has tapped into the massive unemployment situation in Nigeria. Because of the number of idle hands, its ranks grew fast," he said. "The sect is dangerous and constitutes a big threat to the security of this country."