About 250 people have been killed in attacks by the Islamist group Boko Haram -- "Western education is sacrilege" in the Hausa language -- of the largely Muslim north and its increasingly violent offshoot Ansaru, since early April.
The sharp escalation in bloodshed and the military skills displayed by the Islamists in their assaults, including a battle with Nigerian army troops, have worsened the security crisis that threatens to destabilize Africa's top energy producer.
This marks a major intensification of an apparent effort by al-Qaida of the Islamic Maghreb, a group of highly seasoned Islamist fighters that is engaged in heavy fighting French and African troops in Mali, to move southward in sub-Saharan Africa.
This thrust into the heart of the African continent by the jihadists, who are operating across North Africa from Morocco in the west to Egypt's Sinai Peninsula in the east further afield in Somalia, has major strategic implications.
West Africa is already a major oil-producing zone and getting bigger. Much of Nigeria's oil goes to the United States.
East Africa's also emerging as a significant producer of natural gas with major deposits found in the Indian Ocean off Mozambique and Tanzania. Exploratory drilling recently started off South Africa.
Until about a year ago, Boko Haram was primarily a local problem in northeast Nigeria.
The country's population of 150 million is roughly split evenly between the predominantly Muslim north and the overwhelmingly Christian south.
When the group emerged four years ago, seeking to carve out an Islamic state in northern Nigeria, it was armed with bows and poison-tipped arrows and crude motorcycle bombs, and favored setting churches on fire in attacks on regions where Muslims and Christians have become mixed.
But in recent months its operations have been marked by a growing military expertise and new weapons, particularly large numbers of shoulder-fired rocket-propelled grenade launchers.
Western and African security officials say the weapons and the military expertise could only have come from the al-Qaida groups operating in North Africa, another energy-rich region that's become highly unstable since the so-called Arab Spring of
Nigerian and North African security sources said several hundred Boko Haram members underwent military training with AQIM in 2012 around Timbuktu in northern Mali, a region the jihadists, armed with weapons plundered in Libya during its 2011 civil war, seized in 2012.
The first real hint of Boko Haram's new-found military skills came on April 19 when scores of Islamists attacked Baga, a northeastern fishing community on the shores of Lake Chad in Borno State, where Boko Haram first erupted in 2009.
For the first time, Boko Haram used dozens of heavy machine guns and RPGs, creating a wall of fire behind which other units advanced on their targets, a classic infantry maneuver.
In Baga, the Islamists mounted a major assault on Nigerian troops, who apparently were dismayed by the attackers' military capabilities and fire discipline during the 5-hour battle.
Some 185 people were killed, including soldiers, insurgents and civilians. It was one of the bloodiest episodes since Boko Haram rose up.
That attack illustrated the Islamists' new tactical combat skills and their ability for the first time to mount coordinated ground attacks against the Nigerian military and security forces rather than Christian civilians who've been their main targets since the organization emerged four years ago.
On Tuesday, some 200 Islamists descended on the northeastern town of Bama and launched a coordinated assault on an army barracks and the town's prison.
More than 100 prisoners were freed. The army said 22 policemen, 14 prison officers, two soldiers and four civilians were killed. But other sources put the death toll as high as 228.
Human Rights Watch says 3,000 people have been killed since Boko Haram went on the warpath in 2009.
The Islamists are also mimicking their North Africa allies by kidnapping Westerners for ransom.
Boko Haram supposedly received $3.15 million from France for the April 19 for the release of seven French citizens abducted in Cameroon in February.