Gunmen opened fire on a bar in Jos, the capital of Nigeria's restive Plateau state, sparking retaliation from a mob and killing nearly three dozen people in all, local sources said Monday.
Plateau state, in central Nigeria's Middle Belt region, experiences recurring violence in the countryside, mostly linked to land disputes between farmers and herders.
Jos, a religiously mixed city, has seen sectarian violence but deadly, mass casualty attacks in the crowded capital have been rare in recent years.
It was unclear how many people were killed in the Sunday evening shooting in a Jos neighbourhood popular with local university students and staff and how many were killed in the ensuing mob retaliation.
At least 12 people were killed when unidentified attackers opened fire at a bar-cum-restaurant in the Anguwan Rukuba neighbourhood, in the Jos North district, said Plateau state Red Cross secretary Nurudeen Hussaini Magaji.
He later updated the death toll from the shooting and the mob retaliation to 33, without breaking down how many were killed in each incident.
"The attackers shot people at a joint," said Mangalle Idris, a local youth leader.
Then a mob formed, Idris said, and "attacked people that were either passing or doing business and they killed them."
After initially listing the death toll from the mob at 10, he revised that number down to three, with 30 people killed in the gunfire.
"Mob action killed three passersby, two of them were burnt beyond recognition," he said.
The University of Jos said the attack, "and the consequential tensions it has generated", prompted it to postpone exams scheduled for Monday and Tuesday.
The state government said investigations were "ongoing", without giving a toll or naming suspects, and ordered a curfew in Jos North from Sunday to Wednesday.
That same evening as the Plateau attack, unidentified gunmen in the northwestern state of Kaduna killed 13 people at a pre-wedding bachelor party, local and security sources told AFP.
Nigeria's northwest suffers from rural organised crime gangs, locally called "bandits", which kidnap, kill and extort citizens.
In the Plateau state countryside, farmers and herders have been clashing for years over land access, sometimes erupting into massacres where entire villages are emptied out.
Because the violence falls across ethnic lines, some -- including politicians in both Nigeria and the United States -- have characterised the killings as religiously driven, a view rejected by most experts.
Violence has been rare in recent years in Jos, said Malik Samuel, an Abuja-based researcher at the nonprofit Good Governance Africa.
However the city saw deadly sectarian riots in 2001 and 2008 that killed hundreds across religious lines, and remains "a keg of gunpowder", he said.
Samuel said the government was smart to quickly institute a curfew, to halt further reprisals.
"But having a clear identity and motive of the perpetrators will go a long way to dousing whatever tension is simmering in the city," he added.
Posts on social media after the Anguwan Rukuba attack variously blamed -- without evidence -- on herders or "bandits" for targeting a community on Palm Sunday.
The Plateau chapter of Jama'atu Nasril Islam, a Nigerian civil society group, called the attacks a "grave threat to peace and coexistence".
"We urge all citizens to exercise restraint. We must not allow anger and grief to push us into actions that could worsen the situation," it said.
Researchers blame Plateau state's current, mostly rural, crisis on climate change, illegal mining and population growth squeezing available land.
Impunity for killings across rural areas largely abandoned by the state often spark recurrent reprisals.
Local politicians are also known to inflame tensions in Plateau, where the question of which ethnic groups are "indigenous" to the land is politically sensitive.
