French police have released one of the people arrested this week on suspicion of links with the breakaway Irish Republican group, the Real IRA.
Anti-terror officers detained six French nationals from the Brittany area on Tuesday.
This followed the discovery of a cache of arms and ammunition near Dieppe.
One of two Dublin men detained by Irish police at the same time was charged with membership of the IRA on Thursday, while the other man was released.
Gary Roche, 28, was charged with membership of an illegal organisation, namely the IRA, Ireland International reported.
The French news agency AFP said the man freed in France is the chairman of a committee that twins the town of Guingamp in Brittany with Shannon in Ireland.
The suspects, who are said to include one woman, have not been named. AFP says most are in their 50s.
The Real IRA killed 29 people at Omagh
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They are suspected of involvement in a support network for the Real IRA, police sources have told AFP.
A small group of Breton nationalists has previously been found to be backing Spanish Basque militant group Eta, but it is not known whether the suspects in this case are Breton nationalists.
Joint operation
Tuesday's raids are said to have followed a joint investigation by the anti-terrorist division, counter-espionage officers and the intelligence service.
Police netted two submachine guns, an automatic pistol, and two silencers, the Associated Press reported.
They are analysing mobile phones and computers they seized during the arrests, the agency said.
The Real IRA has been blamed for a series of attacks since breaking away from the IRA.
The most serious was the 1998 Omagh bombing, which killed 29 people and was the worst single atrocity in 30 years of violence.
Dissident Republican paramilitaries are opposed to the Northern Ireland peace process and the Good Friday Agreement.