Gardai are investigating after an alleged sighting of a drone by a pilot at Dublin Airport caused flights to be suspended yesterday morning.
It is understood the alleged drone has not been located and no arrests have yet been made.
The drone was spotted over the airfield shortly before 11.30am, with flights subsequently suspended by the Irish Aviation Authority (IAA) for 30 minutes until the runways were deemed safe.
Dublin Airport Authority (DAA) spokeswoman Siobhan O'Donnell said a number of planes were kept in a holding pattern, while two were diverted during the period.
"The decision to suspend flight operations is not taken lightly, it's taken purely for safety reasons. A drone sighting is extremely serious," Ms O'Donnell said.
"The pilot has seen the drone on the airfield while taxiing for take-off, so he got in touch with the Irish Aviation Authority and they took the decision to suspend flight operations, as per the protocol in place.
"That was just after 11.30am. Flights were holding in the holding pattern, two flights were diverted, to Belfast and to Shannon."
She added the DAA will be reviewing the incident with gardaí.
It is illegal to fly a drone within 5km of Dublin Airport and the DAA has signs up around this area to highlight this.
All drones which weigh more than 1kg must be registered with the IAA.
A Garda spokesman said: "Gardaí are investigating the alleged sighting of a drone around the area at Dublin Airport. The matter is under investigation and there are no arrests."
Transport Minister Shane Ross said "we've done what's prudent" by temporarily suspending flights from Dublin Airport over a drone sighting.
Mr Ross described the incident as "a matter of concern" but said the fact the airport reopened swiftly was "encouraging".
"The existing arrangements are in fact that the safety of passengers will be most important, our priority, and that's why the airport's been closed," he said.
Mr Ross said the threat risk group on drones will be sitting again next week.
He added: "We're as prepared as we can be."
However, Mr Ross was criticised by Opposition TD Robert Troy over the issue.
The Fianna Fáil transport spokesman said the situation "could have been more chaotic".
"Minister Ross's previous comments that the likelihood of a drone attack in Ireland was 'low' clearly shows his lack of understanding of the seriousness of the issue," Mr Troy said.
"Following the drone sightings at Gatwick Airport, he was at pains to stress that the regulatory provisions in place in Ireland, which control and restrict the use of drones, were stronger than those of the UK."
In January, Mr Ross called a special meeting of the National Civil Aviation Threat and Risk Group to advise him on the recent incidents in the UK and their implication for Irish airports.