Police identified a Moldovan connection in the first case, and in the second four Bulgarians are due to stand trial in October.
The prosecutor in the red hands affair said it appeared “to be an attempt to destabilise France orchestrated by Russian intelligence”.
Russia and Iran have both been named by French intelligence as countries liable to provoke dissension in France through “dirty tricks”.
Police investigating the latest affair told media that they were approached by a Normandy farmer who said he had sold “about 10” pigs’ heads to two men driving a Serbian-registered car.
The same car was seen in CCTV footage in the Oberkampf region of eastern Paris on Monday evening, and then again near some of the mosques.
Police said tracing of the Croatian mobile phone showed the car crossing into Belgium early on Tuesday morning.
Video footage obtained by news channel BFMTV shows a man in a white T-shirt, cap and surgical mask placing a pig’s head outside a mosque in the south-western suburb of Malakoff. He is seen taking a photograph before leaving, carrying a rucksack.
At roughly the same time another person is seen doing the same at a mosque in the eastern suburb of Montreuil.
In the Stars of David affair, the perpetrators were also seen taking photographs of their work – an act interpreted as a way of proving they had done what they were paid to do, but also to form the basis of a subsequent social media campaign.