French judicial authorities are investigating five people after uncovering an ultra-right plot to attack a religious venue.

A judicial official said Tuesday that two people, one a minor, were arrested and placed under investigation in May for criminal terrorist association. Three others were arrested in the probe that was opened in September in Grenoble, southeast France. The anti-terrorism prosecutor's office took over the case.

The official said only one of the four was being held.

He was confirming portions of a BFMTV report saying that targets were Muslim or Jewish. The official, who requested anonymity because he wasn't authorized to speak publicly, didn't say at what stage the plot was or what the target was.

There was no link with a 2017 ultra-right plot against mosques and migrants.