Yola - President Buhari on Friday ordered security to be tightened at camps for people displaced by the Boko Haram conflict after seven people were killed in a bomb blast.
The explosion happened at the Malkohi camp near the Adamawa state capital Yola just before 11:00 am, when a homemade device left inside a tent went off, the National Emergency Management Agency said.
The attack, which also injured 20 others, bore all the hallmarks of the Islamist militants, who have repeatedly hit "soft" civilian targets in the bloody, six-year insurgency.
Elsewhere in Adamawa, residents in Madagali said a female suicide bomber detonated her explosives at a checkpoint, killing at least two.
There was no immediate confirmation from the authorities, with communications and travel difficult to the remote area in the north of the state.- Extra vigilance -
President Muhammadu Buhari denounced the attack as "heinous and cowardly" and ordered security to be ramped up at all camps.
"We must not let the desperate and evil-minded criminals have any respite," he said in an emailed statement.
"There's now an urgent need for all to (pay the) utmost attention to security issues at all levels - home, work, market, places of worship, schools, etc.
"To defeat terrorism... round-the-clock vigilance is called for."
Security had been tight at the Malkohi camp after hundreds of traumatised women and children held hostage by Boko Haram were brought there after being rescued by the military earlier this year.
Armed soldiers manned the gates and carried out checks on vehicles and passengers, AFP reporters witnessed on a visit to the camp in May.
The sprawling camp, set back from the road, and near an army base, consists of concrete buildings housing dormitories as well as tents outside.
Suleiman Mohammed, director of response, relief and rehabilitation at the Adamawa State Emergency Management Agency (ADSEMA), told AFP there were currently some 3,000 people staying at Malkohi.
Yola had been seen as a relative safe haven from the violence and last year its population more than doubled in size to about 400,000 as those made homeless flocked to the city.
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Many of the displaced were housed at state-run camps or stayed with relatives and friends, reliant on assistance from organisations such as NEMA, the Red Cross and the American University of Nigeria (AUN).
Lionel Rawlings, head of security at the AUN, which is based in Yola, confirmed student volunteers were slightly injured by flying debris.
"None was in direct contact with the explosion but there was flying shrapnel. We dodged the bullet," he said.
NEMA spokesman Sani Datti said: "So far seven persons lost their lives and 20 persons were injured in the bomb blast.
"Among the injured, seven were treated and discharged while 13 persons, including four NEMA officials, are still receiving treatment at (the) Federal Medical Centre, Yola."- 'Hearts of evil' -
Nigeria's former vice-president Atiku Abubakar, who founded the AUN and is from Yola, said in a series of tweets that he was "deeply saddened" by the bombing.
"Only persons with hearts of evil could do this," he wrote.
"The Yola IDP camp is the largest in Nigeria, and is refuge to thousands of people who fled the insurgency from mostly Borno and Yobe (states).
"Today's attack is an attempt to break the spirits of the people who came to seek refuge. The perpetrators will know no peace."
Buhari on Monday said the military was gaining ground in the counter-insurgency, with troops apparently regaining control of captured territory and squeezing militant supply lines.
He has given his new military high command, appointed in early August, three months to end the conflict, which has left at least 15,000 dead and made more than two million homeless since 2009.