The fast food restaurant chain had initially denied after independent testing that its burgers contained horsemeat.
Test results from the plant of its supplier Silvercrest have since confirmed that products from the factory were affected, though Burger King stressed that it has not sold any contaminated burgers.
Burger King stated: "Four samples recently taken from the Silvercrest plant have shown the presence of very small trace levels of equine DNA. This product was never sold to our restaurants.
"Within the last 36 hours, we have established that Silvercrest used a small percentage of beef imported from a non-approved supplier in Poland.
"They promised to deliver 100% British and Irish beef patties and have not done so. This is a clear violation of our specifications, and we have terminated our relationship with them."
There are more than 500 Burger King restaurants in the UK.
Yesterday (January 30), Tesco announced that it had dropped Silvercrest as its supplier.
Earlier this month, a sample from Tesco Everyday Value Beef Burgers was revealed to contain 21.9% horse meat. Lidl, Aldi and Iceland were among several other retailers affected by the scandal.
However, Irish food safety authority FSAI has insisted that the meat is perfectly safe to consume.