The Northern Secretary, Dr John Reid, has announced an independent inquiry into a break-in at the Police Service of Northern Ireland headquarters in Belfast.
It is understood intelligence documents were stolen during the incident at Castlereagh police base. Security sources admit some form of internal involvement is almost certain.
Dr Reid said he would appoint a "distinguished independent figure" to investigate the incident and he was "absolutely determined" to find out what happened.
The review will run parallel with the criminal investigation, which will be led by Det Chief Supt Phil Wright, the most senior detective in Belfast.
"Any breach of national security is a matter of serious concern to me," said Dr Reid.
"The Special Branch of the PSNI is responsible for matters which are crucial not only for the safety of people in Northern Ireland but for national security more generally.
"It is absolutely essential that we establish the facts surrounding this serious incident and do it as quickly as possible and, in addition, ensure in the national interest that all necessary remedial action has been taken."
Three men, one of whom is said to have had an English accent, entered the Special Branch office in the base.
They are said to have assaulted, hooded, and tied up an officer before rifling through drawers and filing cabinets for up to 20 minutes.
They are reported to have taken a bundle of documents. The office would not easily be found so it is likely those involved had intimate knowledge of its location. The men would have to produce some form of identification to pass guards and also know special codes to unlock corridor doors to reach the room.
Documentation stolen may include details on informers. A PSNI spokesman yesterday confirmed documentation was missing but added: "It would be utterly wrong to comment on the detail of this documentation."
The Chief Constable, Sir Ronnie Flanagan, who is retiring in nine days, has referred the matter to the Police Ombudsman who, he said, would keep in close contact with the senior PSNI officer investigating the incident.
The deputy chairman of the Policing Board, Mr Denis Bradley, said: "In this new era of policing and accountability, it is very important the public are assured there will be accountability."
The DUP Policing Board mem- ber, Mr Sammy Wilson, described the situation as very serious. "People who have given information to Special Branch, and understood it was given in the strictest confidence, would have grave concerns," he said.
The SDLP Policing Board member, Mr Joe Byrne, said he hoped the PSNI would soon be able to state what happened and the implications for current investigations.
Sinn Féin's chief whip, Mr Alex Maskey, said elements of the security services were clearly involved and he called for an outside police force to investigate the break-in.