Nigerian troops have arrested a suspect in the Christmas Day bombings that killed at least 44 people, state television reported, as Washington put three Boko Haram leaders on its global terror list.
In the northern State of Kaduna meanwhile, the authorities said late Thursday they would ease a 24-hour curfew imposed following clashes that have left scores dead since the weekend.
The curfew would be eased on Friday and Sunday to allow worshippers to attend prayer services at mosques and churches, officials said.
Suspect Habibu Bama was arrested in Damaturu, the capital of Yobe State, following a shootout with the military joint task force, the Nigerian Television Authority (NTA) reported.
Security sources said he had been shot and wounded.
Bama, a suspected member of Islamist group Boko Haram, had been wanted in connection with the deadly Christmas attack on a church in Madalla, near Abuja, that killed at least 44 people.
Nigerian security forces meanwhile restored calm in Kaduna state, after fresh clashes had rocked an area already under curfew following days of violence that have so far killed at least 106 people.
Clashes between Christians and Muslims late on Wednesday had erupted in areas in and around the city of Kaduna, leaving at least five people dead, according to residents.
"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, had been under a round-the-clock curfew as troops and police patrolled the area.
But officials said late on Thursday that from Friday this would to be lifted between noon (11:00 GMT) and 4:00 pm.
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.
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.
The United States meanwhile 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.
But officials stopped short of designating Boko Haram itself as a terrorist group.
The three designated members are Abubakar Shekau -- widely believed to lead Boko Haram's main Islamist cell - 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.
The violence in Kaduna state began on Sunday with suicide attacks at three churches that killed at least 16 people and sparked reprisals by Christian mobs, who burned mosques and killing dozens of Muslims.
Boko Haram claimed responsibility for the church attacks.
The group has been blamed for bomb and gun attacks, mainly in Nigeria's northeast, that have claimed more than 1,000 lives since mid-2009.
It claimed responsibility for last August's suicide attack on UN headquarters in Abuja that killed 25 people, as well as a suicide attack on the Abuja office of one of the country's most prominent newspapers.
This latest surge in 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 predominantly Christian south.
Boko Haram has killed more than 1,000 people in Africa's most populous country and largest oil producer since mid-2009.