Detectives investigating the dissident republican murder of policeman Ronan Kerr are carrying out searches in Northern Ireland and north west England.
Detectives from the PSNI and officers in Cumbria Constabulary and the north west counter terrorism unit are conducting the operation, a PSNI spokeswoman said.
Catholic new recruit Constable Kerr, 25, was killed in an under-car bomb attack by dissident republicans at his home in Omagh, Co Tyrone, in April last year.
The Northern Ireland searches are in the Omagh area, and those in England are in Cumbria.
A PSNI spokeswoman said: "The search activity is in connection with the wider investigation into the murder of PSNI Constable Ronan Kerr in April 2011 and linked incidents."