At least 46 people have been killed and dozens injured by two bomb explosions in the central Nigerian city of Jos, police say.
The first blast was in a busy market and the second went off outside a nearby hospital.
No group has said it carried out the attack but Boko Haram militants have carried out a spate of recent bombings.
Jos has also seen deadly clashes between Christian and Muslim groups in recent years.
A spokesperson for the regional governor told AFP news agency that most of the victims were women. The market and bus terminal are part of the commercial centre of Jos.
The second blast was some 30 minutes after the first and killed some rescue workers.
Journalist Hassan Ibrahim told the BBC that tension was rising in the area, with youths blocking some roads. Religious leaders are appealing for calm.
The BBC’s Muhammad Kabir Muhammad in the capital Abuja says witnesses at a hospital in Jos saw bodies being brought in that were burned beyond recognition.
A student in Jos, Ayo Tumbe Omeiza, told the BBC: “The second blast was close to me. I tried to get to my car. I was asking for help. I saw a lot of dead people. After the blast people could not stop panicking. People were driving in all directions.”
President Goodluck Jonathan condemned the attack as a “tragic assault on human freedom”.
“President Jonathan assures all Nigerians that the government remains fully committed to winning the war against terror and… will not be cowed by the atrocities of enemies of human progress and civilisation,” his office said.
Although Boko Haram has previously targeted Jos, the capital of Plateau state, the city has been relatively calm for almost two years.
Plateau state lies on the fault-line which divides Nigeria’s largely Muslim north from its mainly Christian south.
The state has witnessed violence blamed on land disputes between semi-nomadic Muslim Fulani herdsmen and mainly Christian Berom farmers.
States of emergency
The Nigerian government is also currently trying to trace more than 200 girls captured by Boko Haram in April from a boarding school in the north-eastern town of Chibok.
The case has shocked the world and prompted foreign powers to send military advisers to assist Nigeria’s army tackle the insurgency.
On Tuesday, parliament approved a six-month extension of a state of emergency in three north-eastern states – Adamawa, Borno and Yobe.
More than 1,000 people have been killed in Boko Haram attacks this year but the government says it has pushed the militants back into their strongholds in Borno.
Boko Haram is fighting to overthrow the government and create an Islamic state.
Nigeria’s violence is not confined to the north.
Earlier this month a car bomb in the capital Abuja killed at least 19 people and injured 60 more.
The explosion happened close to a bus station where at least 70 people died in a bomb blast on 14 April.