The third round of tests carried out since January revealed contamination of Bird's Eye Traditional Spaghetti Bolognese and Beef Lasagne, Taco Bell's ground beef and Brakes' spicy minced beef skewer, the FSA said.
Ten tests on the four products returned results of more than 1% horsemeat, the agency said, and all four have been withdrawn from sale.
On Wednesday furniture giant Ikea is withdrawing wiener sausages in the UK after tests found "indications" of horse meat, just days after it withdrew a batch of its traditional meatballs.
The Swedish company said it was removing the sausages from sale in Britain, France, Spain, Ireland and Portugal after tests confirmed "a few indications of horse meat".
An Ikea spokeswoman said: "Based on some hundred test results that we have received so far, there are a few indications of horse meat. Together with the Swedish supplier in question we have decided to withdraw from sales also the wiener sausages ... from that supplier."
The move came two days after it withdrew Swedish meatballs from stores across Europe and a handful of countries in Asia and the Caribbean after horse meat was discovered by Czech authorities.
But it said the move affected just one batch as a precaution pending further tests, and meatballs would still be available to buy in its stores.
Yesterday it was revealed that traces of horse DNA have been found in beef samples taken from three meat processors in Poland - the first acknowledgement that the country could be a source of the horse meat that fraudulently ended up in products sold as beef across Europe.
Deputy National Veterinarian Janusz Zwiazek said today that the DNA was found in three samples out of 121 tested. They came from plants in central Poland. Some 80 more samples are to be tested.
Mr Zwiazek said that all three cases have been reported to the prosecutors.
US-owned Tex-Mex restaurant chain Taco Bell said that it was "disappointed" to have discovered the horse meat in tests it carried out on beef supplied to its UK restaurants by a sole European supplier.
"We immediately withdrew ground beef from sale in our restaurants, discontinued purchase of that meat, and contacted the Food Standards Agency with this information," it said in a statement.
"We would like to apologise to all of our customers, and we can reassure you that we are working hard to ensure that every precaution is being undertaken to guarantee that we are only supplied with products that meet the high standards we demand."
Birds Eye had already withdrawn the spaghetti bolognese, lasagne and a third ready meal, a shepherd's pie, from sale in Britain and the Republic of Ireland as a precaution after tests found 2% of horse DNA in a chilli con carne dish it sold in Belgium.
They are made by the same Belgian manufacturer, Frigilunch NV.
"No other Birds Eye products have tested positive for horse DNA, nor do they share the same supply chains as Frigilunch NV," the company said in a statement.
"Going forward we are introducing a new ongoing DNA testing programme that will ensure no minced beef meat product can leave our facilities without first having been cleared by DNA testing."
Brakes, which is based in Ashford, Kent, is the supplier for the House of Commons Catering Service and last month it withdrew its steak and kidney pie, beef and onion pie, steak and kidney suet pudding, and beef Italian meatballs as a precaution.
It also supplies pubs among 19,000 customers who buy around 48,000 cases of products containing beef every week.
It too said it was introducing new tests after the discovery, alongside 259 negative tests.
"Our testing programme represents a significant proportion of all results the FSA has obtained from across the food industry," it said.
"Our tests also confirmed one positive equine DNA finding at between 1% and 10% on a Brakes spicy minced beef skewer and one positive test reported by a customer of our subsidiary division Creative Foods, on a lasagne manufactured exclusively for them.
"Brakes have also segregated a frozen burger as a precaution after equine DNA at 1% was reported to the Food Standards Agency.
"Brakes and Creative Foods are very disappointed to have been let down by our respective suppliers and have sincerely apologised to our customers.
"As any responsible company, we have a duty of care to all our customers and the consumers they serve to guarantee the integrity of the products we purchase."
A first wave of tests carried out since the scandal broke found horse meat in products including Aldi's special frozen beef lasagne and special frozen spaghetti bolognese, Co-op frozen quarter-pounder burgers, Findus beef lasagne, Rangeland's catering burger products, and Tesco Value frozen burgers and Value spaghetti bolognese.
A second wave of tests revealed contamination of Asda's chilled beef bolognese sauce, beefburgers, minced beef and halal minced beef sold by Sodexo, which supplies food to schools, care homes and the armed forces, and a Whitbread Group lasagne and beefburger.