Three men remain in custody this morning after eight million cigarettes were found in a container in south Armagh.
Tobacco worth €2.7m was also seized during searches in County Louth.
This joint operation north and south of the border involved gardai, revenue, the PSNI and HM Revenue & Customs.
Seven searches were carried out at a business premises and six homes in the Carlingford area of County Louth yesterday morning.
Around €100,000 in cash was recovered along with raw tobacco worth over €1.5m.
Hand-rolling tobacco packaged for sale worth €1.2m was also seized.
One articulated lorry, one rigid lorry, two trailers and a van were also found, along with mobile fuel-laundering machinery and equipment used for the manufacture of tobacco products.
The men who have been arrested by HM Revenue and Customs are aged 34, 37 and 55.