ATHENS, Greece (AP) _ Police banned all public gatherings in a northern mining region Monday in an effort to quell violent opposition to the construction of a gold processing plant.

Authorities said the step was necessary to keep the Canadian project _ the largest single direct foreign investment in the country _ on track. Opponents of the plant claim it will dampen tourism and harm the environment.

A police announcement sent to community offices bans ``all public meetings, marches, demonstrations, etc.'' in and around the communities of Olympiada and neighboring Varvara until Dec. 4.

``The state is determined to take all called for measures in order for this project to proceed, because it is in the interest of the Greek economy and of the Greek people,'' government spokesman Dimitris Reppas said.

Police who searched a makeshift checkpoint set up by demonstrators found 99 petrol bombs, three barrels of chemicals and some spent bullet casings, authorities said. A police spokesman, who declined to give his name, would not provide more information on the type or amount of chemicals involved.

Four men at the checkpoint, including the president of Olympiada, Nikos Mitsiou, were taken in for questioning, police said.

Residents of several small communities about 40 miles east of Salonica are protesting plans by the Canadian company TVX Gold Inc. to build a gold processing plant at nearby mines.

Toronto-based TVX insists its gold processing will not harm the environment and promises to clean up any pollution left from previous mines.

Constantinos Sinis, president of the company's Greek subsidiary TVX Hellas, said many TVX employees fear harassment by the residents and refuse to work in the area.

Demonstrations on Nov. 11 left nine police injured and caused severe damage to TVX equipment.

The president of a neighboring town, Adonis Stoitisas, said the government clampdown could provoke residents to violence.

``At some stage people will get fed up, and they will revolt,'' he said.

TVX bought the old Kassandra mines from the Greek government in 1995 for about $46 million. Situated in 16,000 acres of forest, the mines have yielded various metals, including zinc and silver, for more than 2,000 years. TVX estimates their gold reserves at 3.4 million ounces.

But the investment has been plagued by problems almost from the start. Residents blockaded area roads last year, shutting down TVX operations for 10 months.