The Georgia peanut plant at the centre of a salmonella outbreak appears to have knowingly shipped tainted products, the U.S. Food and Drug Administration said.

Peanut butter, chopped peanuts and peanut meal that tested positive were shipped out of the Blakely, Ga., plant before follow-up lab tests had determined the products were safe, the food safety agency alleged Friday.

The FDA had previously said that Peanut Corp. of America had retested products after getting a positive result for salmonella and only shipped the goods after follow-up testing came back negative.

The agency amended its inspection report on the plant after a review of documents revealed some inconsistencies, Michael Rogers, the FDA's director of the division of field investigation, told Reuters.

Criminal probe begun

The government has opened a criminal investigation, officials said. U.S. federal law forbids producing or shipping foods under conditions that could make it harmful to consumers' health.

Peanut Corp. has denied any wrongdoing.

A Peanut Corp. lawyer told the Associated Press the company is investigating what happened at the plant and had no comment on the latest FDA findings.

The salmonella outbreak in the U.S. has sickened at least 575 people and appears to be linked to eight deaths.

More than 1,550 products containing peanuts, ground peanuts, peanut paste or peanut butter from the firm's Georgia plant have been recalled in the U.S., while the Canadian Food Inspection Agency has recalled about 170.

With files from the Associated Press