Updated

Ireland says food safety officials have found more horsemeat traces in beef burgers and pinpointed a problem in an imported ingredient, and the meat processing plant has shut its production line in response.

The Irish Agriculture Department announced Thursday night that nine of 13 burgers analyzed Tuesday have tested positive for horse DNA. It says seven ingredients added to the Irish beef also were tested — and only one, imported from another European country, tested positive for horse DNA.

The processing plant at the center of the controversy, Silvercrest Foods in the Irish border county of Monaghan, says it's suspending operations indefinitely pending further investigations into why horsemeat is getting into its products.

Silvercrest is the second-largest producer of frozen beef burgers in Ireland and exports to United Kingdom supermarkets.