Andrew Rhodes, FSA director of operations, said the probe would go on until "there was nothing left to find," The Guardian reported Wednesday.
Environment Secretary Owen Paterson traveled to Brussels for an emergency a meeting of European countries caught in the scandal. He was expected to discuss the growing Europe-wide crisis with the European Commission health and consumer officials and food safety officials from several other countries, the BBC said.
Officers entered Peter Boddy Licensed Slaughterhouse in Todmorden in West Yorkshire and Farmbox Meats Ltd near Aberystwyth in Wales Tuesday to investigate the circumstances in which horse meat was sold as beef in the kebabs and hamburgers.
"The FSA has suspended operations at both these plants," the agency said in a statement, noting that local police were assisting. "The FSA has detained all meat found and seized paperwork, including customer lists from the two companies."
Rhodes said nothing indicated a widespread problem.
"What we are doing is focusing on the areas we think are the highest risk so we have identified documentary evidence that has led us to take the action that we have," Rhodes told the BBC. "We don't have evidence that this is a widespread problem in [Britain]."
He said five slaughterhouses in Britain processed horses regularly, and suspicions about one led to the raid.
The FSA ordered food businesses tests all processed beef products and preliminary results are expected Friday, although full results could take much longer, The Guardian said.
"We're progressing very well through our investigations but they're not complete yet," Rhodes said. "So I'm not going to speculate on what else we might find."