Four people have been arrested in France on suspicion of acquiring weapons "with a view to committing a terrorist act".
The arrests came as part of an investigation into a terrorist conspiracy.
No immediate details on the nature of the planned attack were revealed but a minister described it as "extremely violent".
"We had sufficient evidence to lead us to believe that a major attack was being planned," Interior Minister Christophe Castaner told reporters on Monday.
France has been on high alert since the start of terror attacks began in 2015, leaving more than 250 people dead.

Former US VP Dick Cheney dies at 84
Dozens killed, army helicopter downed as Typhoon Kalmaegi hits Philippines
Trump threatens to cut funds for New York City if Mamdani wins mayoral race
Worker trapped under collapsed medieval tower in Rome dies
Saudi Crown Prince bin Salman to visit Trump in White House
Australia to offer three hours free solar power daily to millions
Man charged with 10 counts of attempted murder after knife attack on UK train
Tanzania's Hassan sworn into office after deadly election violence
