Four men arrested in connection with an attack on an off-duty PSNI officer in Castlederg on Monday are still being held.
The four were arrested at different locations in Co Tyrone on Thursday morning.
Meanwhile, two further arrests were made in the case lastnight. A man and a woman are being held at Antrim police station for questioning.
The 27-year-old Catholic officer suffered serious leg injuries when a device exploded under his car close to the village of Spamount, near Castlederg, Co Tyrone. He was on his way to work at the time. The attack has drawn republican, nationalist and unionist criticism.