An improvised weapon was left in the grounds of a primary school in Belfast, in what a senior police officer has described as an “act of the utmost recklessness”.

Police have launched an investigation into the device, and are linking it with dissident republican terrorists.

They believe it was destined to be used in an attack on officers.

The device was discovered by the principal of Holy Cross Boys Primary School on Monday, while he was helping the caretaker clear an issue with the sewerage system.

Children and staff were evacuated from the premises as police moved in to secure the area.

PSNI Belfast District Commander Jonathan Roberts told a press conference at Musgrave Street police station: “We have recovered what we have at this stage assessed to be an improvised weapon which has the potential to fire a high calibre round.

“Our working theory at this time is that this weapon was most likely to have been left there by dissident republican terrorists and it was probably destined to be used in an attempt to kill or seriously injure police officers who are serving and protecting the community of north Belfast.”

The school is to remain closed on Tuesday while the security operation continues.

Mr Roberts said police want to make sure they are satisfied there is no risk to children in the area.

“I would like to say that this is an act of utmost recklessness and a highly stupid act, the people that have done this do not represent any kind of cause, they do not represent any section of the community.

“What they have done is endanger the lives of children,” he said.

“The device was left in the immediate area where the youngest children would be playing during the course of the school day.

“It’s a very, very dangerous act and I would appeal for anybody who has any information to contact the police.

“Our terrorism investigation unit have launched an investigation into the weapon and its history and who may have built it and who left it there.

“It’s very important, particularly given the circumstances of where it was left, in the immediate area where children were playing, that anyone with information contacts police please.”

School principal Kevin McArevey described the moment he found it as “a scary moment”.

“We had to lift a manhole cover to get the rods down and to my surprise, there was a plastic package just sitting in the sewers,” he told the BBC.

“I lifted it out and imagine my surprise when I opened it up, there was wires at the top of this and tubing in it.

“It was a scary moment for both of us.”

He added: “We had cleared out the sewers three years previous, it was put in there within the last three years.

“Whoever left this device should consider their reckless disregard for the health and wellbeing of the children who would regularly use the nature garden.”

SDLP MLA Nichola Mallon condemned those behind it.

“This is disgraceful. To create a device and then hide it in the grounds of a primary school shows how low these people will go and the complete disregard and disrespect they have for the community,” she said.

“They’re happy to put children, parents and school staff at risk.

“No principal and no school should have to experience this.

“This school is a proud part of the heart of the community in Ardoyne; the boys who go to it are the future.

“The thugs behind this have nothing to offer the people of Ardoyne and they will not drag us back to the past.”