Documents, including a spreadsheet containing the names of more than 200 serving officers and staff, are believed to have been taken from a private vehicle on 6 July.

A police issue laptop and radio are also thought to have been stolen in the theft in Newtownabbey, near Belfast.

Assistant Chief Constable Chris Todd, the Police Service of Northern Ireland's (PSNI) senior information risk owner, said: "We have contacted the officers and staff concerned to make them aware of the incident and an initial notification has been made to the office of the information commissioner regarding the data breach.

"This is an issue we take extremely seriously and as our investigation continues we will keep the Northern Ireland Policing Board and the Information Commissioner's Office updated."

It comes as the PSNI declared a critical incident after a "significant" data breach relating to all 10,000 of its officers and staff.

The force earlier apologised after it inadvertently published the information in response to a Freedom of Information (FOI) request on Tuesday.

The breach included the surname, initials, the rank or grade, the work location and departments of all PSNI staff, but did not involve the officers' and civilians' private addresses.

Northern Ireland's Chief Constable Simon Byrne is to cut short a family holiday to face questions over the two breaches.

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The data is hugely sensitive in Northern Ireland where police officers are still sporadically targeted by dissident groups in bomb and gun attacks, despite a 1998 peace deal largely ending three decades of sectarian violence in the province.

The wife of a serving Northern Ireland police officer has told Sky News they are living in fear after the first breach compromised his details.

In an interview with Sky's senior Ireland correspondent David Blevins, the woman said she found out the PSNI had inadvertently published the information online in a text message from her husband on Tuesday afternoon.

Speaking under the condition of anonymity, the officer's wife said they do not talk about what her husband does for a living outside the family or their immediate circle of trust - and they will now have change the way they live even further.