FRAISSES (AFP) - French workers facing job losses from the closure of a Swedish-owned metals plant were holding four managers captive on Thursday to press demands for better severance pay.

The factory's director, human resources director and two other bosses at the Aker plant in central France were detained Wednesday by workers angry over the shutdown and loss of 120 jobs.

After spending the night in a factory meeting room, the managers were finally released early Thursday evening.

Union officials said the angry workers were demanding a lay-off package of 28,500 euros for each worker but the managers said the Swedish headquarters were refusing to negotiate while the bosses were being held.

"No one has the right to treat us like trash and get rid of us with just 6,000 euros (8,500 dollars)," the sum reportedly on offer, said one worker at the site in Fraisses, southwest of Lyon.

Akers announced three months ago that it planned to shut down the Fraisses plant in June, citing a collapse in customer orders.

French workers last year carried out a series of "bossnappings" to protest layoffs, but no such radical action has been taken over the past months.

President Nicolas Sarkozy in April spoke out against the detentions, saying there were illegal and vowed to take action.