KADUNA, Nigeria (AFP) - Multiple suicide attacks on churches in northern Nigeria and subsequent rioting by Christian youths targeting Muslims killed at least 21 people on Sunday, officials said.
Bomb blasts struck three churches in the northern Kaduna state in the space of an hour, the latest in a string of Sunday attacks that has threatened to ignite wider sectarian strife across the divided country.
There was no immediate claim of responsibility for the bloodshed but the attacks were likely to be blamed on Boko Haram, an extremist group bent on creating an Islamic state and responsible for scores of recent attacks.
Police placed the state under curfew for 24 hours "to assess the situation", leaving Kaduna's seven million inhabitants banned from leaving their homes for a full day.
Two churches were attacked in the city of Zaria and one in Kaduna City, killing at least 16 people, police said, adding all three attacks were carried out by suicide bombers.
After news of the blasts spread, Christian youths took to the main motorway that leads to the capital Abuja, attacking motorists who looked Muslim.
Christian mobs carrying machetes and clubs were also prowling the streets of Kaduna city, denouncing the attacks, a Red Cross official said.
"There were reprisals by Christian youths in areas near the scene of the blast. They moved in large numbers attacking people they believed to be Muslim," said the official who asked for anonymity.
"There were deaths, but I don't have the figures," he added. An AFP reporter said he saw the bodies of 10 people killed by rioters at a morgue.
An official from the National Emergency Management Agency, who also declined to be named said, "the total deaths from the bombings and protests are 21 deaths and 101 injured."
The first blast struck ECWA Goodnews Church in the Wusasa area of Zaria city at 8:35 am. The second explosion went off 10 minutes later at the Christ the King Catholic church in Zaria's Sabongari area, a police statement said.
The third blast hit the Shalom Church in Kaduna city at 9:30.
"A total of 16 persons have so far been confirmed dead as a result of the explosions within the three churches," national police spokesman Frank Mba said in a statement.
A worshipper at the Shalom Church in Kaduna City said the attack was carried out by a suicide bomber.
"I saw a car just drive into the church and right away the car exploded and killed a soldier and two private security guards guarding the church," Joseph Emmanuel told AFP.
Emergency officials had also reported attacks on churches in Nassarawa and Barnawa in the south of the same state but police did not confirm them and the targets of the blasts remained unclear.
The police described the violence by Christian youth mobs that followed the attacks was termed "a momentary break down of law and order."
The police chief urged "criminal elements who have been carrying out campaigns of violence on innocent Nigerians and institutions to desist forthwith," in the statement issued from Abuja.
He also said a massive deployment of forces had been ordered across "every nook and cranny of the state."
One Kaduna said resident said it was not safe to travel.
"I cancelled my trip to Abuja because of the huge number of rioters that have taken over the roads," the man told AFP.
The latest violence targeting Christians in Nigeria, Africa's most populous nation and top oil producer, was swiftly condemned by the Vatican.
"The systematic character (of the attacks) on Sunday is horrible and unacceptable," Vatican spokesman Federico Lombardi told journalists, warning that, if unchecked, the violence could widen and lead to yet more reprisals.
No group has claimed responsibility for the attacks but the church blasts resembled those previously claimed by Boko Haram, responsible for more than 1,000 deaths since mid-2009.
The Islamist group claimed a suicide bombing at a church in Bauchi State that killed at least 15 earlier this month.
Nigeria's population of 160 million is roughly divided between a mainly-Muslim north and predominantly Christian south.