French counter-terror police arrested 10 members of a group on Tuesday which French media have called “ultra right”, as an investigation source says they planned to attack French politicians, mosques, and immigrants.

Police investigations had unmasked “intentions to commit violent action” of which the details remained unclear, a judicial source said, but that involved “a place of worship, a politician, a migrant, drug traffickers”. The arrests took place in the Paris suburb Seine-Saint-Denis and in Marseille throughout the day on Tuesday, reports Le Figaro.

A French police source has named one of the politicians targeted by the group as government spokesman Christophe Castaner. Another plot to kill a politician referred to radical left leader Jean-Luc Mélenchon, but it is reported this ambition was abandoned after he failed to reach the presidential election second round in May.

The suspects, taken into custody for “association with terrorist wrongdoers”, were also thought to be plotting to target migrants as well as mosques. “They were only in the earliest planning stages,” one source said.

Aged between 17 and 25 years old, the arrests included nine men and one woman, all of whom are suspected of having links to 21-year-old Logan Alexandre Nisin, who was arrested in June. La Provence reported Nisin was suspected of having “assaulted” left-wing activists during a protest, of having glorified Norwegian mass murderer Anders Breivik, and of threatening to kill among others “blacks, migrants, scoundrels, [and] jihadists” in online posts.

French police said at the time of his arrest Nisin had no “specific action plan”, but his “threats were clear”, and that he was in possession of two pistols and one other firearm.

Agence France Presse contributed to this report.