It was discovered by a passing police patrol near Holy Cross Boys' Primary School in Ardoyne in the early hours of Sunday morning.
Ch Supt Chris Noble said the device was "sizeable" and an attempt by dissident republicans to kill police officers.
He said the lives of the local community had also been put at risk.
"There's no doubt that device was there to try and kill community police officers on the beat in their local area but also it was left in such a reckless manner and in such a reckless location that it would undoubtedly have led to the death or serious injury of a member of the public had it exploded anywhere near them," he said.
"This is an attempt, we believe, by violent dissident republicans to kill police officers but it was also very much an "anti-community act" as well, in terms of where it was located and the way in which it was left."
About 20 residents had to leave their homes during the security operation and were given shelter in a nearby community centre.
The senior officer said they included "very distressed young children" as well as elderly residents and people with "significant disabilities".
They have since been allowed to return home.
The bomb was left outside the gates of Holy Cross Boys' Primary School
The chairman of the NI Police Federation Mark Lindsay, said the attackers wanted to murder or maim officers.
"They didn't care if passers-by or children out playing in the area were caught up in an explosion. It was an entirely reckless act," he said.
"This appears to have been a deadly, anti-personnel-type weapon. Thankfully, it was recovered and removed without being detonated.
"The attackers are terrorising people who live in the area and preventing them from getting on with their everyday lives."
Northern Ireland Secretary of State, James Brokenshire, said: "I am sickened by this incident with dissident republican terrorists placing a bomb close to a primary school in north Belfast.
"This shows their wanton disregard for human life, potentially putting children in danger.
"The consequences could have been utterly devastating and it shows them for what they really are."
North Belfast MP, Nigel Dodds of the Democratic Unionist Party (DUP) said: "Those who constructed and planted this device clearly have no regard for any human life.
"Such a device could have caused devastation and we must all pay tribute to the work of those who have made the scene safe."
The Sinn Féin North Belfast MLA, Gerry Kelly, also condemned those who had left the bomb in the area.
"Those who are involved in this need to get off the people's backs and they need to go away," he said.
"The message is as simple and straightforward as that, we could have been dealing with death here, thankfully, we're not."
The Sinn Féin North Belfast MLA, Gerry Kelly, condemned those who had left the bomb in the area
SDLP councillor Paul McCusker said the incident had caused distress to those living in the area.
"In total there were over 20 homes evacuated," he said.
"One young girl, a six-year-old, you could see the fear when you were speaking to her and she said [was] woken up by her mum and had to leave the house.
"She told me she actually thought she was dreaming and her and her mum were very frightened."
The chair of the Policing Board, Anne Connolly, urged witnesses to help detectives track down those responsible.
'Leaving an explosive device in the heart of the community shows the recklessness of those responsible as anyone could have been caught up in this," she said.
"I'm grateful that the device was found and the attempt to harm our police officers thwarted."
The school's vice-principal, Chris Donnelly, said: "There was a device that had been left at the entrance to the school which is obviously very disconcerting for people who had to be taken from their beds and moved."
He added that a lot of young people gather in the area in the evening.
Pupils are due to return to Holy Cross on Monday after the Easter break.