An "irregular" software issue was to blame for most of Ireland's airspace being temporarily closed earlier this week, officials have said.

A back-up system was deployed on Tuesday night when air traffic control in Shannon and Cork failed.

The problem led to the brief suspension of flights at the two airports, although Dublin Airport was not impacted.

Following a 'thorough investigation', the Irish Aviation Authority says the issue was not related to radar - as had initially been reported by the airports themselves - but was instead a software problem.

Operations have now been transferred back to the primary system, which has been fully restored.

In a statement, the IAA explained: "When the technical issue occurred on Tuesday evening, we are satisfied that the back-up system and contingency planning worked as required.

"This ensured that we restored full service in a safe and timely manner and disruption to aircraft was minimal."

It adds that full radar coverage was 'maintained at all times'.