Update: Gardaí have seized "a substantial quantity of ammunition" and a mortar tube in an operation investigating dissident Republican groups in Co Louth.
Officers started the search this morning near Omeath on the Cooley peninsula.
Gardaí said they "have recovered a substantial quantity of ammunition of varied calibre along with a mortar tube".
The Army Bomb Disposal team are at the site and a cordon is in place, with the search expected to continue into tomorrow.
No arrests have been made.
By Elaine Keogh
Gardaí are believed to have found what could be weapons, possibly belonging to dissident republicans, in what is being described as a "significant" operation.
Gardaí have requested the Army Bomb Disposal team to attend the scene of the search in the Cooley Peninsula area of Co. Louth.
The operation is understood to be in the general area of Omeath
Gardaí say the operation is live and ongoing and involves the Special Detective Unit. Among other things, it is responsible for investigating threats to State security.
No other details are available at the moment.