Gardaí from Bruff and the divisional drugs squad under Det Sgt Con McCarthy found cocaine with a street value of €400,000 when they raided a house in Murroe.
A man from the city who moved to Murroe was recently was arrested.
A pump-action shotgun and a handgun were found when gardaí raided a house in St Senan’s Street, St Mary’s Park.
Two men arrested are being held under section 30 of the Offences Against the State Act.
Gardaí arrested two juveniles in the Ballynanty area after petrol was poured through the letterbox of a house.
In follow-up searches, a sawn-off shotgun was found.
Gardaí are also investigating two arson attacks in which houses in College Avenue, Moyross, and Clarina Avenue, Ballinacurra Weston, were very badly damaged.
Mayor Kevin Kiely condemned the attack.
“The incident in Moyross happened in broad daylight. Someone saw what happened.
“Members of the public are going to have to come forward and give information to the gardaí,” said Mayor Kiely.
“I would appeal to the public to give them information. It is the only way we are going to catch these criminals.”
He said his heart went out to the families whose homes have been destroyed.