Irish MPs have condemned an "utterly shocking" unauthorised plane stop by a Royal Air Force (RAF) transport aircraft, which has been labelled a "serious" incident.

The Hercules transport plane refuelled at Shannon Airport, in County Clare, on Ireland's west coast, but was not given clearance before landing.

As a neutral country, RAF chiefs should have asked for permission from Irish authorities beforehand and given assurances that the aircraft had no weapons, ammunition or explosives.

According to official policy, it should also have been made clear that the plane was not on an intelligence-gathering mission or military exercise or operation.

British military chiefs could be reprimanded over the incident on 29 December which campaigners have described as a "total affront to Irish sovereignty".

British diplomats blamed a "communication breakdown" and said the Hercules was unarmed and not in official operation at the time of the landing.

The RAF landed 21 aircraft at the airport last year and followed the correct procedure on each of those occasions.

Ireland's foreign affairs minister Charlie Flanagan was quoted as saying by RTE: "The government views breaches of the procedures set down for the granting of permission for such landings with the utmost seriousness.

"I have instructed my officials to discuss the matter further with the British embassy with a view to ensuring that correct procedures are followed in future."

In a parliamentary question, Clare Daly, an Independent politician from Dublin who campaigns against any foreign military using the airport, revealed the unauthorised stopover:

"It is utterly shocking that a foreign military aircraft landed without permission from the department of foreign affairs on Irish soil.

"This is a total affront to our sovereignty and any notion of neutrality. The minister should be before the Dail [Irish parliament], apologising and assuring us of the measures he has put in place to prevent a recurrence."

Flanagan added: "The embassy has confirmed in writing that the purpose of the landing was refuelling, and that the flight was unarmed; carried no arms, ammunition or explosives; and was not engaged in intelligence-gathering nor formed part of a military exercise or operation."

Since 2002 over 2.5 million US troops are estimated to have gone through Shannon Airport en-route to destinations such as Afghanistan and Iraq.