Testing carried out by Powys County Council has shown three samples of beef burgers made by catering supplier The Burger Manufacturing Company (BMC) have tested positive for horse meat.
Further work is being carried out to establish exactly how much horse meat these products contained and to test for the presence of the veterinary medicine phenylbutazone, or bute.
BMC is withdrawing the products from sale while it contacts customers to inform them of the results of the tests.
Yesterday as part of its investigation into mislabelling, the Food Standards Agency carried out a test on a quantity of frozen products detained in Northern Ireland.
Silvercoat was the supplier of the beef burgers and were identified in a survey carried out by the FSA in Ireland.
Of the 12 samples from the suspect consignment that have been tested, two of the samples came back positive for horse meat, at around 80%. The investigation into the traceability of these raw materials and their source is under way. As this meat was detained, it has not entered the food chain.
Retailers have confirmed to Environment Secretary Owen Paterson that they expect the majority of their tests on processed beef products to be completed by Friday.
Retailers and the British Retail Consortium (BRC) met Paterson for the first time since test results covering 65% of the targeted products were published Friday.
Speaking after the meeting, the BRC also said that retailers are doing all they can to engage with consumers on the issue and establish the extent and causes of failures in the supply chain.
The last report said five brands tested positive for horse meat against the Food Standards Agency's threshold. These are the five own brand products that have already been notified to the FSA and withdrawn from sale over the same period.
British Retail Consortium Director General Helen Dickinson said: "Test results have continued to come in over the weekend. The labs are working flat out and our members are confident that the vast majority of testing will be completed by Friday.
"We were very pleased that the Secretary of State recognised the hard work of retailers in progressing their testing programmes so quickly.
"Retailers take their responsibilities very seriously and are doing everything they can to maintain consumer confidence and increase surveillance.