A fresh wave of British army intelligence officers have been deployed in Derry to combat the increasing activity of the Real IRA and Oglaigh na hEireann.
On Sunday, a detachment of British army intelligence special operations troops arrived in the city.
The new deployment comes in response to last week’s Real IRA bombing of a bank in the city.
Derry is believed to be the most spied upon city in any major western democracy.
Security was significantly increased around Derry Airport on Sunday in preparation for the arrival of the new specialist units from an RAF base in Britain.
It is not known which branch of British intelligence is involved.
Both the British army and PSNI refused to confirm or deny the arrival of the detachment.
Last year Deputy First Minister Martin McGuinness described the deployment of the British Army’s Special Reconnaissance Regiment (SRR) in the north as a “major threat” and described their deployment as “stupid and dangerous”.
He said the history of the SAS, the SRR and other such covert military groups in Ireland showed theyposed the biggest threat to the public.
Last year, the British Army openly searched a house in the Creggan area of the city alongside the PSNI police. A search document presented listed members of a “military search troop”, as well as one member of a mysterious organisation, the ‘MCFA’.
The new deployment comes as the PSNI, in tandem with th Gardai in the 26 Counties launched a major operation across Ireland, with surprise checkpoints, raids and searches.