Four men are being questioned after ammunition was seized during a car search.
A number of 9mm rounds were recovered during the operation at Summerfield, in Youghal, Co Cork.
It is understood the men - a teenager, one in his 20s, and two in their 30s - were arrested as part of a criminal investigation.
The car they were travelling in was stopped in Youghal just before 5pm yesterday.
They are being detained at Fermoy, Youghal,and Middleton Garda stations under section 30 of the Offences against the State Act.
Follow-up searches are continuing in the area.