Gardai and customs officers have seized two shipments of high purity cocaine with a potential street value of more than €4m.
The swoop came after a surveillance operation lasting more than three weeks.
Last night a mother and daughter were in garda custody and being questioned about the seizures.
Undercover gardai had been keeping watch on a Dublin city hotel since before Christmas as inquiries were being carried out into the planned arrival of the shipments into the country.
The two seizures amounted to 15kg of cocaine, with a conservative street value of €1,050,000.
The cocaine has not been analysed but its high purity suggests that it could have been cut and mixed four times before being sold, indicating a street value of up to €4.2m.
Garda surveillance teams kept watch on a hotel on the northside of the river Liffey and armed officers moved in yesterday evening and found one of the two shipments, which had arrived here from the Caribbean.
The second shipment was captured at Dublin Airport and had originated in Mexico.
After the hotel seizure, gardai arrested two Caribbean women, a mother and daughter, aged in their late 40s and early 20s.
Both were taken to Finglas garda station for questioning under the drug trafficking legislation, which allows the gardai to hold them without charge for up to seven days.