Police said attackers threw a "low-capacity" bomb into an Arabic school in a drive-by attack in Nigeria's mainly Christian south, wounding six children and an adult on Tuesday evening. Nobody has claimed responsibility.
The attack followed Christmas Day bombings blamed on the Islamist Boko Haram group that killed 40 people in several towns - the deadliest an explosion outside a Catholic church near the capital Abuja.
The president of the Christian Association of Nigeria, Reverend Ayo Oritsejafor, urged followers on Wednesday not to take revenge but said they should defend themselves, their property and their places of worship "any way they can".
"The consensus is that the Christian community nationwide will be left with no other option than to respond appropriately if there are any further attacks on our members, churches and property," Oritsejafor told reporters.
As frustration rose over the state's seeming inability to stop attacks despite military crackdowns, President Goodluck Jonathan said: "we are doing our best" with the assistance of African and other countries that have experienced extremist attacks in the past.
"... we will restructure, we will readjust and make sure that we get a team that will meet with this challenge that we are facing today," he said, adding that arrests had been made and "interrogation is being done".
Jonathan urged Nigerians not to shield the culprits.
"The terrorists are human beings, they are not spirits. They live with us, they dine with us. So we know them, people know them. And as long as Nigerians are committed to exposing them, we [will] get over this ugly situation."
Nigerian leaders have been seeking to calm tensions amid fears the Christmas attacks could set off sectarian clashes in Africa's most populous nation and largest oil producer. The country is roughly divided between a mainly Muslim north and predominately Christian south.
It was not clear who was behind the bomb attack on the Arabic school in Delta state in the oil-producing Niger Delta region.
Police spokesman Charles Mouka said it occurred while a group of children between the ages of five and eight attended evening Arabic and Koranic lessons.
While scores of explosions have hit the Delta region in recent years, they have mainly targeted oil installations and the attacks have not been of a sectarian character.
Christian leaders urged the government and intelligence authorities to take action against spiralling violence blamed on Boko Haram, and Oritsejafor labelled the attacks "a declaration of war on Christians and Nigeria as an entity".
He said Christians should protect themselves "any way they can".
Also on Wednesday, a coalition of Nigerian Pentecostal churches said they would defend themselves if the authorities failed to do so, though an official stressed they were not advocating taking up arms.
"In the year 2012, if these unprovoked attacks continue and Christians remain unprotected by the security agencies, then we will have no choice but to defend our lives and property," the Pentecostal Fellowship of Nigeria said.
"Retaliation not the answer"
Nigeria's top Muslim spiritual leader met Jonathan over the attacks on Tuesday, stating afterwards that the violence did not signal a religious conflict.
"I want to assure all Nigerians that there is no conflict between Muslims and Christians, between Islam and Christianity," Sultan of Sokoto Muhammad Sa'ad Abubakar told journalists.
"It's a conflict between evil people and good people. The good people are more than the evil ones, so the good people must come together to defeat the evil ones, and that is the message."
The president's national security adviser urged Christians not to seek revenge.
"Retaliation is not the answer, because if you retaliate, at what point will it end? Nigeria must survive as a nation," Owoye Azazi said.
Violence had been raging even in the days before the Christmas bombings, especially in the northeastern cities of Damaturu, Potiskum and Maiduguri. Most of the incidents attributed to Boko Haram have occurred in the northeast.
Officials were rushing to provide relief to some 90 000 people displaced in Damaturu after clashes last week between Boko Haram and security forces.
Up to 100 people were feared killed in Damaturu, a police source and rights group said.
"We advised the displaced against moving into any temporary camp for security reasons, therefore most of them are sheltering in the homes of friends and relatives in the city and neighbouring villages," said Ibrahim Farinloye of the National Emergency Management Agency.