Police said they found ammonium nitrate and other substances
French police have seized hundreds of kilos of bomb-making ingredients in a garage in the south-eastern city of Grenoble, officials have said.
Police suspect the cache of at least 300kg (660lb) of ammonium nitrate and other explosive substances may belong to the Basque separatist group, Eta.
The chemicals were found by chance on Sunday by the owner of the garage.
Eta is blamed for the deaths of more than 820 people in its 40-year campaign for an independent Basque nation.
Last week, a court in Paris sentenced a Spanish woman to 14 years in prison after finding her guilty of running a cell based in France that identified targets for the group.
The owner of the garage in Grenoble said he had decided to break open its lock at the weekend because he had not received any rent in three months.
"I found some bags, I opened one of them which contained white powder and straight away I informed the police," he told the AFP news agency.
He said he had advertised the garage on the internet and that he had met the tenant only once, when he signed the lease in December. Police said they believe the tenant gave a false name.
In 2007, a similar cache of potentially explosive substances were discovered in an Eta base in the southern French town of Cahors.