Police in Northern Ireland said they had arrested five men on Tuesday in a major operation in connection with the car bomb murder of a Catholic police officer in April.
"Police investigating the murder of Constable Ronan Kerr... almost four months ago have mounted a major search and arrest operation," said a statement from the Police Service of Northern Ireland (PSNI)
"Five suspects were arrested under the Terrorism Act," it added, in an operation that involved about 200 police officers and searches at seven locations in the British province.
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New police recruit Kerr, 25, was killed in the April 2 bomb attack in the town of Omagh, which was also the site of a 1998 bombing that left 29 people dead.
The killing was blamed on dissident republicans seeking to knock Northern Ireland's peace process off course and came just before elections to the devolved legislature in Belfast, which passed off peacefully.
The five men arrested Tuesday, ranging in age from 22 to 46, were taken for questioning to the town of Antrim, said the PSNI. Several people had already been detained in the weeks after the murder.
Searches linked to the arrests were taking place in parts of County Tyrone, with vehicles, computers, mobile phones and clothes seized and removed for forensic analysis, police said.
Detective Superintendent Raymond Murray of the PSNI said the arrests showed that the investigation was making progress.
"Our determination to pursue every possible line of enquiry remains undiminished," he said in a statement.
Northern Ireland's three decades of unrest known as The Troubles were largely ended by peace accords in 1998, although violence still flares up occasionally and the past two years has seen an upsurge in attacks.
The unrest pitted Catholic republicans opposed to rule from London against Protestant unionists.
Some of the worst sectarian violence in years erupted in the province last month around a Catholic enclave in mainly Protestant east Belfast, with rioters hurling petrol bombs at police, who responded with water cannon.
