British and Irish officials say they fear police informants in Northern Ireland may be killed after a break-in at police intelligence headquarters in Belfast.
British officials say little is known so far about the break-in and theft of documents at the east Belfast headquarters of the police intelligence unit, known as the special branch.
The special branch has relied heavily on informants during three decades of investigating sectarian violence between Northern Ireland's Catholic and Protestant paramilitaries.
Britain's Northern Ireland secretary, John Reid, told parliament in London that while the investigation of Sunday's break-in proceeds, lives are at stake. "Any breach of national security is a matter of grave concern," he said. " The work undertaken by special branch, police service of Northern Ireland, bears directly on the safety of lives both in Northern Ireland and throughout the United Kingdom more generally."
The Conservative Party spokesman on Northern Ireland, Quentin Davis, told parliament undercover police agents must fear for their lives. "Agents who think they may have been exposed will face the agonizing dilemma of whether to flee the province, thereby perhaps increasing the suspicion of them, or to stay there, risking their lives," he said.
In Dublin, the Irish Prime Minister Bertie Ahern said he had spoken to British Prime Minister Tony Blair to express his concern about the safety of police informants.
The British government has appointed a former senior civil servant in Northern Ireland, John Chilcott, to lead a special investigation into the security breach.