PARIS (Reuters) -- Olympique Marseille are threatening to boycott Sunday's Ligue 1 match against archrivals Paris St. Germain because of fears over crowd trouble.

"PSG are guilty on two accounts; they are refusing to provide 500 tickets we have ordered and have sold them to their own fans who will be seated just above our own supporters," Marseille chairman Pape Diouf told sports daily L'Equipe.

"This proximity is potentially explosive. It's sheer madness and incompetence but we are not the puppets of PSG and we could decide not to play," he added.

"That's what we should have done last year when our team bus was attacked by PSG supporters who smashed his windows."

Matches between PSG and OM are always regarded as high-risk games. Security will be particularly tight around the Parc des Princes today after rival groups of PSG supporters fought each other and ransacked a motorway service station on their way back from a match last weekend.

The game, which was due to kick off at 2000 GMT, has already been brought forward four hours for security reasons.

The 48,000 spectators will be searched and some 1,200 policemen will be deployed around the stadium, which will only be opened to ticket-holders.

Marseille lie fifth in the table on 43 points, 16 adrift of leaders Olympique Lyon. PSG are eighth with 41 points.