In France, consumer affairs minister, Benoit Hamon, has also ordered an immediate investigation and said results will be available by midweek.
In a statement, Hamon said a provider in Luxembourg and traders in Cyprus and the Netherlands were part of the chain being probed.
The Swedish National Food Agency has announced it is reporting Findus to police, which is the standard course of action when products have been sold with the wrong labels.
European Union officials plan to meet in Brussels to discuss the issue on Wednesday February 13.
How has the public reacted?
The revelations have revolted many meat eaters in the United Kingdom, where horse meat is generally considered taboo, although it is commonly eaten in neighboring France, as well as countries including China, Russia, Kazakhstan and Italy.
January's discovery of pig DNA in beef products is of particular concern to Jews and Muslims, whose dietary laws forbid the consumption of pork products.
Jewish dietary laws also ban the eating of horse meat.