British prime minister David Cameron has ordered an investigation into the contamination of Irish-produced beef burgers containing horse meat.
The burgers were on sale in supermarkets Tesco and Iceland in the UK.
Mr Cameron said retailers had to take responsibility for what was a "completely unacceptable state of affairs".
He told MPs he ordered the Food Standards Agency to conduct an "urgent" investigation into the "extremely disturbing" case.
Speaking at prime minister’s questions in Westminster, Mr Cameron said there needed to be a full investigation
The discovery of horse meat in supermarket beefburgers is "extremely disturbing" and "completely unacceptable", he said.
"They will be meeting retailers and processors this afternoon. They will be working with them to investigate the supply chain.
"But it is worth making the point that ultimately retailers have to be responsible for what they sell and where it has come from."
"It is a very important issue and it is an extremely serious issue. People in our country would have been very concerned to read this morning
that when they thought they were buying beefburgers they were buying something that had horse meat.
The Food Safety Agency had " made clear there is no risk to public safety because there is no food safety risk but this is a completely unacceptable state of affairs", he said.
The UK's Food Standards Agency (FSA) said has been in contact with retailers and producers named in the survey by the Food Safety Authority of Ireland, which discovered the contamination.
It has "called a meeting this afternoon with a wider range of food industry representatives to discover the extent of the potential problem and to investigate how this contamination might have occurred,” it said in a statement.
PA