Five people were arrested on Monday night in southern France with a dangerous amount of explosives, a local investigator said on Tuesday.
Four of the men aging from 24 to 37-years-old were held in the town of Saint-Jean-de-Vedas, near Montpellier and one was picked up in Béziers, around 70km away.
The five suspects, Russian nationals from Chechnya, were placed in custody in Béziers and their homes have been searched, prosecutor Yvon Calvet said earlier in the day.
The prosecutor said certain "products" had been recovered during their searches, without giving further details.
The prosecutor added however that the investigation was in its early stages and authorities were yet to establish whether or not a specific attack was planned.
Gilles Soulier, judicial police director of the southern city of Montpellier, told French media on Tuesday that: "There is no known attack plan. It is a case which has no religious connotation but it is organised crime."
Soulier said they had a dangerous amount of explosives in their possession.
According to the regional newspaper Midi Libre, "a cache explosives" was discovered not far from the Sauclières stadium on Béziers.
The newspapers police sources said firefighters were sent to the scene as a precaution. It also claimed that 100 grams of TATP explosives were found in apartment in Béziers . That is the same kind of substance that were used in the Boston marathon bombing.
One of those arrested lives in Béziers and another "probably" in the Mediterranean city of Montpellier, said the prosecutor.
Investigators are trying to find the addresses of three other individuals held in custody.
According to Midi Libre one of those held was implicated in a 2008 bombing in Montpellier, which left several people injured.
The arrests come as France remains on high alert following three days of attacks by jihadists earlier this month in Paris that left 17 dead.
Le Progres newspaper reported on Tuesday of another counter-terrorism operation in Lyon, last September, which saw two brothers arrested when police feared they were ready to mount an attack.
Chechnya stages huge protest against Muhammad cartoons
Chechnya is a restive republic in the Caucasus region to the south of Russia, with a largely Muslim population. It has been labelled as a breeding ground for terrorism and in recent years separatist Islamist rebels have launched attacks in Russia, with whom the region has fought two wars of independence in the past two decades.
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The two men accused of carrying out the bomb attack on the Boston marathon were of Chechen origin.
On Monday several hundred thousand people joined a state-organised rally in the Chechen capital Grozny against cartoons of the Prophet Muhammad published by Charlie Hebdo, with Russia's interior ministry putting the number at 800,000.
"This is a protest against those who support the publication of caricaturesof the Prophet Mohammed," Ramzan Kadyrov, who has ruled Chechnya with an iron fist since being installed by President Vladimir Putin a decade ago, told the demonstrators.
Kadyrov has turned Chechnya, where tens of thousands of civilians were killed in two Kremlin wars to crush a separatist movement, into a showcase of loyalty to Putin.
Kadyrov attacked the French government for backing Charlie Hebdo magazine's right to run a Mohammed cartoon on its front cover a week after two Islamist gunmen -- saying they were avenging the publication of previous Muhammad caricatures -- massacred 12 people in an attack on its office in Paris.
"We say firmly that we will never allow anyone to go unpunished for insulting the name of the prophet and our religion," Kadyrov said.