A statement from the Police Service of Northern Ireland said:
Detectives from the PSNI's Serious Crime Branch, with assistance from officers in Cumbria Constabulary and the North West Counter Terrorism Unit, are conducting a number of searches in Northern Ireland and north west England.
The search activity is in connection with the wider investigation into the murder of PSNI Constable Ronan Kerr in April 2011 and linked incidents.
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Cold, foggy and frosty overnight. Mainly dry to start the new working week
Kerrie brings you Saturday's forecast for Cumbria & The Scottish Borders
Another cold and icy night but cloudier, wetter, windier and milder from the west by dawn