Who are Nigeria's Mend oil militants?
The Movement for the Emancipation of the Niger Delta (Mend) is a loose web of armed groups in Nigeria's oil-producing Niger Delta region.
These gangs have spent years kidnapping oil workers, attacking oil fields, blowing up pipelines and fighting Nigeria's army.
Niger Delta politicians originally created the gangs - by arming young men to use as their private armies and to rig elections.
But later, the young men began to turn the guns on the government, and oil companies, organising into a militant movement, under the banner Mend.
They demand that the Delta receive more benefits from its oil, with a fairer share of the wealth invested in roads, schools, hospitals, clean water and power supply.
The Delta is impoverished - in spite of five decades of oil extraction.
But Mend's gangs also run criminal rackets - kidnapping civilians for ransom, and making billions of dollars by stealing crude oil from pipelines.
In the past, they have cut Nigeria's oil production by one-third - causing spikes in the global oil price.
The group was successful, partly because of a sophisticated media strategy.
A shadowy figure, who signed himself "Jomo Gbomo", creates headlines by sending journalists dramatic e-mails - either promising attacks, or denouncing Nigeria's government.
Some security experts believed "Jomo Gbomo" to be Henry Okah, until he was imprisoned, accused of gun-running.
Their authorship today is unclear.
But at present, the Mend web is split.
Nearly all the senior commanders in the field - and their foot soldiers - have accepted an amnesty, and are observing a ceasefire.
One small faction has not. That group is presumed to be behind the Abuja car bombs.
That faction continues to send e-mails to the media - claiming to speak for the whole of Mend - to the irritation of the senior figures on ceasefire.