A chance alert by a local tradesman has exposed a terror-linked bomb plot to target banks, French Interior Minister Gérard Collomb has revealed.
Police were called on Wednesday to a flat in the southern Paris suburb of Villejuif, where they found 100g (3.5 oz) of TATP explosives and chemicals.
Three men have been arrested.
The interior minister said the suspects had denied any terrorist motives but he added that they had been in phone contact with people in Syria.
"They wanted to blow up banks with the TATP, but what we're seeing is that they were linked to terrorists, so it's more in that direction that we have to look," he told FranceInfo TV.
TATP (triacetone triperoxide) has been widely used in jihadist attacks because it is relatively easy to produce.
The explosives would have been used to target counters inside the banks for cash, Mr Collomb added. Hours after he spoke, police found more explosive materials in a garage rented by one of the suspects at Thiais, a few kilometres south of Villejuif.
The alarm was raised by a locksmith or plumber working at the block of flats on Wednesday morning. When he spotted suspicious objects inside a tent on a balcony he called police, who discovered a type of bomb factory. Gas canisters, bottles of chemicals and electrical wiring were also found.
Two suspects, aged 36 and 47 and of North African origin, were quickly arrested in a neighbouring area, and a third man was detained overnight. The first two arrested were not previously known to authorities, while the third suspect was said to have been radicalised and on a watch list.
France has suffered a spate of attacks in recent years. Jihadists who attacked Paris in 2015 also used TATP.
More recently traces of it were found last month in the rubble of a house in north-eastern Spain on the eve of the 17 August Barcelona attack. Catalan police believe the jihadists had been planning to use explosives from the house as part of the Barcelona plot.
Mr Collomb declined to speculate on whether the latest discovery was linked to Barcelona but said it was possible.
However, investigators know that Younes Abouyaaqoub and one or two other jihadists had driven to the Paris area days before the attacks. Their Audi A3 car was caught by a speed camera south of Paris on 12 August.
They stayed at a hotel in the Malakoff area a few kilometres to the north-east of Villejuif and the interior minister said it was now clear that they had visited the Eiffel Tower on two occasions during their visit.
"We know they go to buy a camera, we know particularly they leave the hotel in the evening and they go off to spend a long time in front of the Eiffel Tower. Then they go back there the next day before setting off for Spain," he said, citing a study of the men's mobile phone geo-location.
When asked about a potential link to the Villejuif bomb factory discovery, Mr Collomb said Spain was widely known as a conduit for groups based in Morocco but beyond that he could not say.