Police investigating allegations of a multi-million pound fraud surrounding Ministry of Defence contracts have carried out a series of searches.
Documents and computer equipment were seized in the raids at commercial premises in Belfast, Lisburn, Newtownabbey and Antrim.
A private residence in Downpatrick was also searched during the operation.
The raids involved 120 MoD police officers, 50 PSNI officers and 50 staff from the Serious Fraud Office.
No arrests were made during the seven searches.
A MoD spokesman said the searches, which began at 0730 BST on Wednesday, were connected to suspected fraud involving a group of civil servants and others. He added that all involved were from Northern Ireland.
It is understood the inquiry centres on suspected fraud surrounding MoD building contracts handled by civil servants which date from the 1990s to the present.
No military personnel are thought to be involved.
The raids were linked to a series of searches which were carried out in Northern Ireland in January 2004.
The officer in charge of the operation, Detective Chief Superintendent Rob Allen from the Ministry of Defence fraud squad, said warrants had been executed at six business premises and one residence.
"We are investigating a small number of civil servants within the Ministry of Defence and some contracting companies," he said.
"The suspicions are that civil servants have colluded with contractors to defraud the Ministry of Defence.
"These are defence contracts here in Northern Ireland, relating to building services.
"We have taken away a number of documents and computers for further analysis."