The official number has now soared to 355 from 42 last week.

"We have started an investigation," a spokeswoman for the public prosecutor's office told Reuters.

Prosecutors will work with the General Inspection Service and the Agriculture Ministry to determine whether any farmers or feed makers should face criminal charges.

Belgian prosecutors are investigating the bankrupt Belgian firm Bioland as a possible source of the contamination with MPA hormone, which experts believe can cause infertility in humans.

The number of affected farms ballooned this week when it was discovered that MPA was supplied not only to farmers who mix their own pig food, but also to commercial feed makers, Agriculture Ministry spokesman Benno Bruggink said.

Some 55 pig farms out of 2,000 who make their own feed received glucose syrup laced with MPA as a raw material while 74 feed companies which also got shipments of contaminated ingredients delivered feed to another 300 pig farms, he said.

UNDER CONTROL

Agriculture Minister Laurens-Jan Brinkhorst has assured the European Union that the situation was under control after Brussels demanded more action to seal off farms and feed makers.

"All batches of MPA have been traced and from today no more contaminated feed will be produced and no pigs that have consumed high-risk levels of MPA will come onto the market," he wrote in a letter to EU Health Commissioner David Byrne.

All 355 farms are under supervision and only when inspectors rule that the farms and pigs are free from all contamination will the regulations be lifted, he added.

The scandal, which has now spread beyond animal feed to soft drinks, is one of many to hit Europe in recent years, from Britain's mad cow and foot-and-mouth woes to a case of contamination of food with cancer-causing dioxin in Belgium.

Belgium's health food safety agency AFSCA said on Tuesday it had found MPA traces in materials Bioland supplied to two soft drink firms.

While the feed contamination occurred more recently, the last shipments of these soft drinks syrups were in May 2001 and the agency believed people had already consumed the drinks.

Belgian Health Minister Magda Aelvoet told parliament this week Bioland imported waste from an Irish drugs company, but said proper notification procedures had not been followed.

Unlisted Bioland went bankrupt in early May and was not registered with AFSCA. Bioland's telephone has been disconnected and company executives could not be reached for comment.

MPA, or Medroxyprogesterone-acetate, is banned in the European Union. All products that contain it must be destroyed.