Police with guns will patrol Belfast City Airport

It comes as airports throughout the UK are becoming increasingly concerned about the threat of international terrorism.

At least two officers from the Police Service of Northern Ireland have been trained as sky marshals, and may be deployed on any UK flights, amid continuing fears about air travel to the United States.

Belfast City Airport said the change to full-time armed police was to meet government guidelines.

Security has always been a priority at the airport with searches and checks on a routine basis.

Government vigilant

But the harbour police - which patrolled the east Belfast airport on a part-time basis - did not carry guns in the past.

Those officers had not routinely patrolled the airport site or walked into the terminal building.

Police at Belfast International Airport in County Antrim have been armed for more than 30 years.

The City of Derry Airport would not discuss security but said the situation was constantly under review and if there was a change they would make it public.

The government said it was being vigilant, that the security forces were vigilant and it would encourage passengers to continue using air travel as normal.

Just before Christmas, it was announced that the state of alert in the US was being stepped up in response to a substantial increase in intelligence reports about possible threats.

Airline security was increased, amid reports that extremists were interested in using aircraft to stage an attack as they did on 11 September 2001.