A total of three people held in France as suspected Real IRA dissidents have now been freed, officials say.
Three others arrested at the same time are being held in Paris ahead of a possible court hearing.
They are being detained at the headquarters of the anti-terrorist DNAT force, officials say.
One report from French news agency AFP said one of the three remaining in custody was in hospital after being taken ill.
The six were held after raids in Brittany and Normandy earlier this week.
A small cache of arms was also found buried in woods outside the port town of Dieppe.
Police were given until Saturday to release the suspects or place them under investigation, after a judge extended their detention.
Two other people were arrested in Ireland as part of the same operation.
One was charged with membership of the IRA, while the other man was released.
French police who carried out the arrests said they were investigating a possible support network for the Real IRA.
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 including unborn twins. It 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.