The arrests by anti-terror police of suspects aged 17-25 were part of an investigation into far-right activists, the source said.
The nine men and one woman are suspected of links to Logan Alexandre Nisin, a former militant of the far-right group Action Francaise Provence who was arrested in June, the source said.
Another source named the targeted politicians as government spokesman Christophe Castaner and radical left leader Jean-Luc Melenchon.
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.
A 21-year-old former Action Francaise member was charged in July after making threatening posts on social networks against migrants and jihadists, the sources said.
Nisin was arrested near Marseille on June 28 after posting that he planned to attack blacks, jihadists, migrants and "scum".
Local prosecutors took up the case initially before the anti-terror prosecutors took it over.
One of the probe sources said investigators had determined that Nisin, who possessed arms and practised shooting, had the intention of following through with his threats.
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