Four men and two women were questioned last night by police in the North investigating the financing of a transatlantic IRA gun-smuggling operation. They were held after raids on houses in Belfast and north Antrim.
Officers carried out raids in the latest phase of an investigation in the US, Britain and Ireland into huge arms importation by the Provisionals after declaring their ceasefire was restored.
Some of the smuggled rifles, shotguns and pistols are still missing but security sources last night said the focus at this stage in the three-year investigation was on how the operation was funded.
The operation that led to yesterday's arrests dates back to 1999 when guns and component parts were discovered by postal staff in Coventry. Police in Belfast said yesterday that those weapons had been posted from the US, often in boxes containing toys, before being intercepted in England.
As part of the operation, four people were convicted in Florida of firearms offences in September 2000.
Later a number of the weapons turned up in the Republic, where four men were jailed for guns offences last month.
A Police Service of Northern Ireland (PSNI) spokesman confirmed the force had now taken the lead role in the investigation.
He added: "Some of the weapons believed to have been bought in Florida, including rifles, shotguns and handguns, are still outstanding. Around 100 weapons and ammunition have been transferred by law enforcement agencies in America to the PSNI as part of the investigation."
Mr Conor Murphy, Sinn Féin's Newry and Armagh MLA, claimed the arrests were a planned and co-ordinated attempt to discredit republicans.
He said: "Events like today reinforce clearly in the minds of the nationalist community just how far the current policing arrangements have to go before we achieve a policing service without the malign influence of Special Branch at its core."
Meanwhile, seven men and a woman were questioned by police investigating racketeering and robberies linked to loyalist paramilitaries in Derry.
Efforts to recruit teenagers into the terrorist organisations were also at the centre of the arrest operation, security sources said.
A dozen properties were raided in the Waterside area of Derry and in Ballymoney, north Antrim. It is understood those arrested include several senior loyalists in the north west.
Senior police officers said both the Ulster Defence Association and the Ulster Volunteers had been targeted. "These loyalist organisations have been recruiting youngsters and getting involved in everything from drugs to robberies and intimidation."