There was panic as the device exploded
John Reid has cut short his holiday following the third day of violence outside Holy Cross Girls' Primary School in the Ardoyne area.
Four police officers were injured as they escorted children to the school after loyalist protesters set off a blast bomb on Wednesday morning.
Three men have been arrested following the attack, which has led to calls for a resolution of the school dispute.
There was panic as the device exploded close to the children and their parents walking to school through a police cordon on the Ardoyne Road.
The group of about 80 pupils and their parents were being stoned by a loyalist crowd at the Glenbryn estate, and as the police moved in a device, believed to have been a blast bomb, exploded.
The Red Hand Defenders, a cover name which has been used by the loyalist paramilitary UDA and LVF, said they carried out the attack.
Dr Reid said the protests had to stop immediately and dialogue had to begin.
"Any legitimate grievances of protesters have been drowned out by this violent sectarian bigotry," he said.
"Children should not have to pay the price of the failure of adults to live together in peace.
"The people of Northern Ireland will not allow themselves to be drawn back towards barbarism."
John White from the Ulster Democratic Party, which is linked to the UDA, has called on loyalist paramilitaries to stay away from the protest.
"I believe, that the residents there have a right to protest in a peaceful and dignified way and they be allowed to do that," he said.
Parents of children at the school are meeting to discuss the situation.
Northern Ireland Security Minister Jane Kennedy has held meetings with political representatives from the area to discuss the violence.
In a statement following the meetings, she called for an immediate end to the violence.
"Everyone I met agreed that the violence was utterly deplorable and must end, if a lasting solution in everyone's interest is to be reached," she said.
The Irish Prime Minister, Bertie Ahern, has decribed the situation in Ardoyne as "tragic, shameful and deplorable".
Earlier the chairman of the school's board of governors, Father Aidan Troy, said the bomb "gives me nightmares to think that this could have been a four-year-old girl who had been hit".
Head teacher of Holy Cross Ann Tanney said the attack was "the antithesis" of everything the school had been working to achieve.
Philomena Flood, who was walking with her seven-year-old daughter, Erinn, when the bomb exploded, said: "It was absolute chaos.
"As the blast bomb went off, we just ran around in circles there were children everywhere we were trying to grab our own and get to the school."
The security forces had been bringing the children and their parents to school past loyalist protesters for the third day, following further overnight rioting in north Belfast.
For three days the police and army have set up a cordon of barriers to bring pupils safely into the school.
Residents from loyalist Glenbryn estate have been attempting to stop the children, from a nationalist area of Ardoyne, getting up the road.
The loyalists are protesting against alleged attacks on their homes.
North Belfast Progressive Unionist Party assembly member Billy Hutchinson said: "I am totally ashamed to be a loyalist today after seeing these people attack young Catholic girls."
The SDLP leader, John Hume, said: "I think the people who are doing this can not be called human.
"I would like to see all the representatives of the unionist community coming together to condemn this."
The Presbyterian Moderator, Dr Alastair Dunlop said violence could have two reactions.
"Either people thrown their hands up and retrench further or it can be such a shock to the system and ask where this is going to lead," he said.
"So I hope people will enter into meaningful dialogue."
In a statement, Protestant Concerned residents of Upper Ardoyne said they wanted to continue a "peaceful protest" and called on their supporters to show restraint.
Sinn Fein assembly member Gerry Kelly said loyalist paramilitaries had deliberately escalated the situation.
"The focus of all the attention must be on the UDA," he said.
DUP North Belfast MP Nigel Dodds appealed to people intent on violence to stay away from the school and said it was now desperately important to resolve the situation.
The children and their parents left the school on Wednesday afternoon, at the end of the school day, and returned along the Ardoyne Road without incident.
Parents were handed a letter from the school's board of governors which has held an emergency meeting over the issue.
The letter said the board would continue to provide education for the children and that the safety of children was at the centre of all their deliberations.
