Boko Haram fighters have waged new attacks on a series of towns and villages, killing at least 160 people.
Early on Friday morning, at least 11 men were dragged from their homes in the village of Miringa by Boko Haram and shot for escaping forced conscription by their group, residents said.
In another set of attacks earlier on Thursday, two girls wrapped with explosives blew themselves up at a crowded market and a military checkpoint in Malari, outside Maiduguri, killing at least 13 people.
The violence on Thursday and Friday morning came just hours after Boko Haram fighters murdered around 145 worshippers in the town of Kukawa, just as they were preparing to open their fast.
Reacting to the series of attacks in the northeastern states, President Buhari said the violence highlighted the need “to form a more effective international coalition against insurgency and terrorism in Nigeria and neighbouring countries.”
Residents described how the fighters entered the homes and executed the men in Miringa.
Baballe Mohammed, a resident in the village, said the gunmen came to the village around 1.30am on Friday morning. They “picked 13 men from selected homes and took them to the Eid prayer ground outside the village where they opened fire on them,” he said, adding two managed to escape.
“The victims were well targeted because they were all residents of Gwargware village… who fled to Miringa some months ago to escape forced conscription by Boko Haram.”
Al Jazeera's Yvonne Ndege, reporting from Abuja, said Boko Haram had embarked on a “really bloody 72 hours in Borno State”, and the worst of the attacks had taken place in Kukawa, 180km northeast of Maiduguri, the biggest city in northeast Nigeria.
The spate of attacks follow a directive from the Islamic State of Iraq and the Levant (ISIL) group for fighters to increase attacks during Ramadan.
Boko Haram this year became ISIL's West African franchise.
The Nigerian group, whose birthplace is Maiduguri, often defiles mosques where it believes imams espouse too moderate a form of Islam.
An estimated 13,000 people killed in the 6-year-old insurgency.
Amnesty International puts the toll at 17,000 dead. Another 1.5 million people have been driven from their homes.
