The leader of Nigeria's Boko Haram has said recent killings of Christians were justifiable revenge attacks and President Goodluck Jonathan had no power to stop the radical group's attacks, in the first video of him posted online.
Boko Haram, whose name translates from the northern Hausa language as "Western education is sinful", has been behind almost daily killings in its home base in the largely Muslim northeast, most recently targeting Christians.
"Christians, everyone knows what they have done to us and Muslims ... we were attacked and we decided to defend ourselves and, because we were on the right path, Allah has made us stronger," Abubakar Shekau says in Hausa in a 15-minute video posted on YouTube, sat in front of two Kalashnikov rifles and wearing a camouflage bullet proof jacket.
"Jonathan, (you) know full well that this thing is beyond your powers," he added, referring to the president.
Shekau is understood to have taken over control of Boko Haram, which wants sharia law more widely applied across Africa's most populous nation, after the sect's founder Mohammed Yusuf was killed in police custody in 2009 following an uprising in which 700 people were killed.
"Everyone knows how our leader was murdered and everyone knows the way the Muslims were killed," Shekau says, remaining stony faced and calm throughout.
"Catastrophe is caused by unbelief, unrest is unbelief, injustice is unbelief, democracy is unbelief and the constitution is unbelief."
Ethnic and religious violence in various parts of the country has added to the chaos caused by the removal of fuel subsidy in a country roughly divided between a mainly Muslim north and the predominantly Christian south.
Twenty people were killed in four separate incidents in the last few days.
Meanwhile, tens of thousands of Nigerians have defied an order to end a three-day-old strike as unions threatened oil production and a mob rampaged in one city, leaving a police officer dead.
The strike over soaring fuel prices sank Africa's largest crude producer further into crisis.
Despite a government order late on Tuesday that labelled the strike illegal and threatened to withhold pay, protesters took to the streets as gangs of youths burnt tyres and harassed drivers for cash.
Pockets of Lagos, the largest city in Africa's most populous nation, descended into chaos, including one upscale neighbourhood, with gangs attacking a police car with sticks and ripping down signposts.
The main groups of protesters in Lagos remained peaceful, however, with about 10,000 people at one of the largest demonstrations dancing and singing anti-government songs.
Some vowed they would begin camping out there.
"I am here with my water and toothbrush because we are not leaving this arena until our demand for fuel at 65 naira [$0.40] is met," said Akinola Oyebode, a 23-year-old at the main protest in Lagos.
He was referring to the price of a litre of petrol before government subsidies were controversially scrapped from January 1.
"We shall not be intimidated by the police because our protest is legitimate and constitutional."
In the central city of Minna, a mob went on the rampage, burning political offices, leaving a police officer dead and prompting an all-day curfew. The cause of the violence was not immediately clear.
In Kano, the largest city in the north, a massive crowd thought to be in the tens of thousands marched through the streets.
Oil production has so far not been affected by the strike, but workers threatened action if the government does not respond to their demands.
"We hereby direct all production platforms to be on red alert in preparation for total production shutdown," said Babatunde Ogun, PENGASSAN union president, in a statement as union officials met in the oil hub of Port Harcourt.
The other oil workers' union, NUPENG, also threatened a shutdown.