A Dublin primary school had to close and send all the pupils home after a security alert in which threats were made against two young children.
Gardaí believe the incident is connected to a feud in the capital involving a number of different groups.
Pipe and petrol-bomb attacks have been carried out in previous months as part of the dispute.
Extra patrols have been ordered to the area, and are expected to continue next week when schools are back after the mid-term break.
The alert at the school in south central Dublin happened last Friday morning when an anonymous phone call was made, saying two young children were going to be targeted.
A separate call was made a short time later and warned that the school building was going to be burnt down.
“The school made a decision to send all children home over security concerns and gardaí were also notified of the phone calls,” a source said.
Gardaí attended at the school and maintained a presence there until all the children left. Locals reported seeing several patrol cars at the scene on Friday.
The Irish Independent understands that the school’s decision to send children home was not made in consultation with gardaí, but following staff discussions over security concerns.
In a separate incident last week, masked men armed with knives arrived at a secondary school searching for a teenage student.
Detectives believe both incidents are linked to the same dispute between groups based in south central Dublin.
Another source said: “There have been serious incidents connected to this dispute in recent months, and it is of extreme concern that innocent young children are now being brought in to this.
“It’s a complex feud involving a number of different groupings and alignments and there are real concerns that this incident could escalate things.”
Incidents that have been connected to the dispute include a fire-bombing in Drimnagh last July that resulted in a young man being hospitalised with serious injuries.
A suspected retaliation incident happened in the same month when a purported pipe bomb was left outside a south inner-city apartment.
The Drimnagh property was targeted again weeks later. It had just been renovated when a pipe-bomb was thrown into the house.
Detectives suspect the men involved in the dispute have links to the murder of Joshua Itseli, who was shot dead in Crumlin last May.
Gardaí believe Itseli and his associates were on their way to carry out a pipe-bomb attack when they were intercepted by a rival gang.
During the ensuing chaos, one of Itseli’s associates fired a rifle, accidentally striking the 20-year-old and killing him.
A murder investigation is continuing into that shooting, but no charges have been brought against the suspect.