Nine people have been arrested by police investigating a number of arson attacks on the homes of serving police officers.
A number of officers in Gilford, Banbridge and Portadown had their vehicles and homes set on fire and, in some cases, destroyed between April and July last year.
Det Insp Keith Gawley described the attacks on the officers as "serious and life-endangering".
He appealed for information.
The arrests on Tuesday followed searches at houses in Larne, Armagh, Banbridge and Craigavon.
A number of items were taken away for examination.
The chairman of the Police Federation for Northern Ireland, Mark Lindsay, condemned the attacks.
"We've seen far too many attacks on the homes of officers. Families have been left traumatised," he said.
"Fortunately, no-one was injured. They are a clear attempt to bully, intimidate and terrorise, but they won't succeed."
The six men and three women are being questioned at Musgrave police station.
They have been arrested on suspicion of a range of offences, including arson with intent to endanger lives, theft, conspiracy to cause an explosion and possession of controlled drugs.
Det Insp Gawley said the police investigation was also focused on "offences involving drugs".