In the biggest of several coordinated raids targeting IRA money-laundering operations across the Republic of Ireland, police said they recovered at least $4.4 million during a raid on one house in the village of Farran, 10 miles west of the southwest city of Cork.
Police also seized approximately $155,000 at one property in the Douglas section of Cork City. Police arrested three men and a woman in the Cork-area raids but did not specify where each occurred.
Police said the operation began Wednesday night with the arrests of three men at Dublin's Heuston train station.
Detectives trailed a suspected major money-launderer from Cork who, after stepping off the train in Dublin, allegedly was caught delivering a suitcase containing $122,000 in laundered euro notes to two men from Londonderry, Northern Ireland.
A team of more than 100 detectives, including specialists from the national force's fraud squad and criminal assets section, had planned the raids for weeks in hopes of finding the $50 million stolen Dec. 20 from the main cash vault of Northern Bank in Belfast, police said.
Detectives backed by forensic teams were expected to search several other properties in the Cork area, all of which have been secured, in the coming hours.
Police could not immediately confirm whether any of the seized money was stolen from the Northern Bank. They said the $155,000 recovered in the Douglas raid consisted of Northern Bank-produced notes.
"This is a massive operation, and our top priority must be first and foremost to finish the searches at hand before we examine the cash itself in greater detail," one detective told The Associated Press on condition of anonymity.
Officers would not begin comparing serial numbers on the seized cash with the records provided by Northern Ireland police until at least Friday, he said. About two-thirds of the cash stolen from Northern Bank was in newly minted notes bearing the bank's distinctive design.
Forensic specialists first must comb the seized cash for possible fingerprint or other evidence, which could take weeks, he said.
If the cash recovered Thursday is from the Northern Bank, it would mark the first police breakthrough since the robbery. Police chiefs in both parts of Ireland have blamed the outlawed IRA but failed to recover any of the cash or charge anyone in connection with the robbery before Thursday.
Police, in keeping with usual practice, refused to identify any of the arrested people by name. Under Irish law, all seven can be interrogated without charge until Friday night or Saturday morning.
Sinn Fein declined immediate comment. The party previously has stressed it believes IRA denials of involvement in the robbery.
But the British and Irish governments and all other political parties in both parts of Ireland have blamed the IRA, which is Ireland's most proficient robber of banks.
The operation involved months of planning. Gangs with inside knowledge of the Northern Bank's operations held hostage the families of two key security employees of the bank, forcing the employees to empty the main cash vault after closing time. The alarm was not raised until hours after the robbers' getaway, when the wife of one coerced bank worker stumbled out of a forest south of Belfast.
Spokesmen for the police forces in both the Irish Republic and Northern Ireland cautioned that, while the Northern Bank raid was the focus for the raids, some or even all of the money seized could ultimately be linked to other IRA rackets.
The modern IRA, founded in December 1969 in Northern Ireland, for decades has run an ever-expanding range of criminal enterprises, including robbing banks and armored cars; counterfeiting bank notes and goods; and smuggling fuel and cigarettes. Anti-racketeering authorities estimate that the IRA generates at least $13 million in illegal revenues annually.