Three men were questioned today about a blast bomb attack on a police station in Co Tyrone.
They were detained in Strabane as British army explosives experts were called in to check suspect devices found close to an hotel in Derry where Chief Constable Sir Hugh Orde had been due to speak.
The men were arrested by detectives investigating the attack on the police station a fortnight ago when neighbouring houses were slightly damaged. Nobody was hurt.
It was believed to have been carried out by dissident republicans, who were also blamed for today's security alert in Derry.
Two suspect devices were found close to the Tower Hotel at The Diamond. A third was discovered not far away in Great James Street. All were described as "elaborate hoaxes".
Sir Hugh had been due to speak at a debate on policing in the hotel tonight, but last night the organisers of Gas Yard Feile, a local community festival, called it off.