The Romanian government is investigating if horsemeat discovered in beef products in Britain and France came from an abattoir in Romania.
Officials said they would take action if laws had been broken.
The chairman of the Commons food and rural affairs committee, Anne McIntosh, has called for a temporary ban on meat imports from the EU.
But the shadow environment secretary, Mary Creagh, said that was not the answer to the problem.
Environment Secretary Owen Patterson said: "This is a conspiracy against the public. It's either gross incompetence or an international criminal conspiracy."
He said the British government was determined to "get to the bottom of it" and was working closely with other European governments, but he said a moratorium was not allowed under EU rules.
Findus, which has taken its frozen beef lasagnes off shelves after some were found to have up to 100% horse meat in them, has said it will file suit in the French courts, believing itself to be the victim of fraud.
But the company that supplied the meat, Spanghero, based in southern France, has also said it was the victim of fraud - and intends to sue the Romanian supplier of the meat.
Six French supermarket chains - Carrefour, Monoprix, Auchan, Casino, Cora and Picard - have also withdrawn ready meals made by Findus and Comigel.
Health Secretary Jeremy Hunt said he was confident patients eating food in hospitals were not being put at risk.
He told the BBC: "All hospitals have a responsibility to make sure the food they're serving is safe.
"We don't believe at the moment that there are public safety issues - there may be fraud issues in terms of people eating something that isn't what the label on the tin says it is. "
Miss McIntosh, Conservative MP for Thirsk and Malton in North Yorkshire, told BBC Breakfast: "None of our meat, none of our slaughterhouses, are implicated and we should be buying as local as possible and we should be buying fresh meat from the butcher, farm shop and supermarket."
She said she wanted a temporary ban on all processed or frozen meat from the EU and said: "I believe there should be a moratorium on the movement of all meat until such time as we can trace the source of contamination."
But Mrs Creagh said a ban on EU meat imports would have "the whiff of panic" and she said: "We need a measured, controlled response to this and it's got to be proportionate.
"What the government hasn't done is get a grip, get the tests on the burgers that were withdrawn three weeks ago out. We could have tested those. If they'd tested them, they could have reassured the public. What they've done is sit on their hands and now they're totally behind the curve."
The BBC's Paris correspondent Hugh Schofield said the scandal had cast light on the bewildering complexity of the food business in the EU.
He said: "A Swedish brand - Findus - supplying British supermarkets employed a French company, Comigel, to make its ready meals.
"To get meat for its factory in Luxembourg, Comigel called on the services of another French firm Spanghero. It used an agent in Cyprus, who in turn used an agent in the Netherlands, who placed the order at an abattoir in Romania."
Our correspondent said: "That extraordinary Europe-wide chain of instructions has now been identified by the French anti-fraud office, which is piecing together how so much horsemeat masquerading as beef entered the food chain."
The French minister for consumer affairs Benoit Hamon said it appeared financial gain was the motive of the fraud and overall it could have netted the perpetrators £250,000.
Horsemeat in France is not noticeably cheaper than beef, but according to the Green MEP Jose Bove the price of horse meat has recently fallen dramatically in Romania following a new law there banning horses-and-carts on the highway.
He said this could have opened tempting possibilities for cheating.
Romania's National Sanitary Veterinary and Food Safety Authority representative Constantin Savu said: "As far as we know there was horse meat provided from Romania, but this doesn't raise any problem, because we have more than 25 abattoirs authorised not only to butcher horse meat but also to export it within the EU."
He said: "We have in these abattoirs officially authorised veterinarians that assist and control the technological process from receiving the animals until the meat is ready to go out of the abattoir. They have certified papers and put official stamps on the meat until it exits the abattoir."
Mr Savu said: "There is no problem with the fact that we export the horsemeat but we cannot know what happens to it on its way to export, after it exits the abattoir."
He said they have begun an investigation to establish what happened but he said: "We have commercial papers for the meat, they are so many that they cannot be counterfeited.
"There is no possibility of changing the sort of the meat within the abattoirs."
On Saturday the food minister David Heath said people should not throw away frozen meat products in the wake of further revelations in the horsemeat scandal.
He advised consumers to carry on eating meat unless told otherwise.
The Food Standards Agency has asked UK firms to test all processed beef foods, but said it did not "suspect there is any health issue with frozen food"