Nigerian security forces sought to restore calm in parts of the country's north Thursday after fresh clashes rocked an area already under curfew following days of violence that killed 106 people.
Meanwhile, the US government said it had designated the head of the main branch of Nigerian Islamist group Boko Haram a "global terrorist" along with two others tied to both Boko Haram and Al-Qaeda's north African branch.
The new clashes late Wednesday between Christians and Muslims hit areas in and around the city of Kaduna, leaving at least five people dead, according to residents.
Police confirmed more rioting, but did not provide casualty figures.
Factors said to have led to the new clashes included the circulation of inciteful SMS messages, an argument at a market that escalated into violence and residents' reactions after claiming the mangled bodies of relatives.
"The clashes started from unfounded rumours being bandied about on text messages of attacks and counter-attacks in the city, which provoked so much sentiment," said police spokesman Aminu Lawan.
Kaduna state, where the violence began on Sunday, remained under a round-the-clock curfew as troops and police patrolled the area.
Kaduna city, the capital of the state of the same name, is a major city in Nigeria's mainly Muslim north and has a large Christian population.
"Soldiers and policemen have deployed in the town, but five people have already been killed in the violence on both sides," said a resident of Kujama, outside of Kaduna. "I saw five dead bodies from the clash."
The 24-hour curfew was however relaxed in the northeastern city of Damaturu, where clashes between security forces and suspected Islamists Monday and Tuesday killed at least 40 and stranded residents unable to return home or access food.
Damaturu residents will now be allowed to move around between 10:00 am and 4:00 pm, the state government announced.
The violence has sparked fears of further reprisals and wider conflict in the country of some 160 million people, roughly divided between a mainly Muslim north and predominately Christian south.
Frustration over the government's inability to stop attacks by Boko Haram, whose insurgency has killed hundreds, has led to warnings that there could be more cases of residents taking the law into their own hands.
There have been calls in the United States for the government there to label Boko Haram as a terrorist group.
Officials stopped short of that on Thursday, but labeled three militant figures as "global terrorists".
The three are Abubakar Shekau, widely believed to lead Boko Haram's main Islamist cell, as well as Abubakar Adam Kambar and Khalid al-Barnawi, alleged to have links to both Boko Haram and Al-Qaeda in the Islamic Maghreb.
The US designation freezes any US assets they may have and bars US citizens from "engaging in transactions with or for the benefit of these individuals," a statement said.
This week's violence began on Sunday with suicide attacks at three churches in Kaduna state, which left at least 16 people dead and sparked reprisals by Christian mobs who burned mosques and targeted Muslims, killing dozens.
Boko Haram claimed responsibility for the church attacks.
While a curfew and heavy security patrols stopped rioting that broke out on Sunday, flare-ups hit the area in the days after.
Separately on Monday and Tuesday, gun battles broke out between suspected Boko Haram members and security forces in Damaturu, previously hit by heavy violence blamed on the Islamists.
Government officials were said to be consulting with religious leaders in Kaduna in an effort to ease tensions.
"We are talking both of conventional law enforcement strategies as well as what I would call a soft approach to conflict resolution," said national police spokesman Frank Mba.
Boko Haram has killed more than 1,000 people in Africa's most populous country and largest oil producer since mid-2009.