LONDON Britain braced itself Saturday for food shortages at the supermarkets, as an outbreak of foot-and-mouth disease in pigs spread and the government imposed a countrywide ban on all movement of farm animals.

The week-long ban from Friday closed down all British livestock markets and abattoirs, prohibited hunting and also halted imports of live animals.

The worst fears of government vets were confirmed as the number of sites where foot-and-mouth (FMD) has been identified rose to six.

It also emerged that at one farm in the northeast the infection had been present for "two to three weeks," -- longer than previously thought and enough time for it to have spread the length and breadth of the country.

Some of the major supermarket chains warned that the outbreak and the ban on transporting animals could lead to a shortage of food on their shelves but urged shoppers not to panic buy, AFP reported.

Agriculture Minister Nick Brown appealed to consumers: "Don't alter your shopping patterns."

A spokeswoman for the Somerfield supermarket chain said: "We are telling customers in our stores that there could be a shortage of meat and to bear with us."

Unveiling the new ban on animal transportation, Brown said: "There is going to be a complete standstill for the next seven days in the movement of livestock in Great Britain."

"The purpose is to prevent the spread of foot-and-mouth disease while we are trying to extinguish it.

"The disease appears to have been present for two to three weeks," Brown added. "The chief veterinary officer has advised me that there is a real risk that FMD could appear anywhere in the UK."

He appealed to the public: "Don't go out on to farms where livestock is found."

Brown also said he had not ruled out the mass slaughter of all livestock within a set distance of farms where outbreaks have taken place.

But he added that Britain's chief vet was not in favour of such a step at the moment.

Cattle and pigs were slaughtered on Friday at all six locations with confirmed cases of FMD -- which is harmless to humans but causes illness in hooved animals like sheep, pigs and cows.

As questions started to be asked about who was to blame for the outbreak and why it had taken so long to detect the virus, Agriculture Ministry officials said they believed a farm in the northeast, at heddon-on-the-wall, Northumberland, was the source of the outbreak.

An Agriculture Ministry spokeswoman said the farm was visited by state veterinary officials on December 22 and January 24 after an anonymous complaint about animal welfare.

But the visit produced no grounds for prosecution and the pigs were "fit and healthy" although the farmer was given advice on upkeep and conditions.

Brown told the BBC: "It is far too early to start allocating blame and it is absolutely outrageous to suggest that state veterinary inspectors wouldn't be able to spot foot-and-mouth disease."

The Opposition Conservative Party's Spokesman on Agriculture, Tim Yeo, said the fact the infection had been present at least two weeks was "extremely worrying and typical of the (Agriculture Ministry's) dithering attitude to agricultural crises."

The pig farmer believed to be at the Center of the Outbreak, Bobby Waugh, 55, said in a statement: "I honestly hadn't seen anything wrong with any of my pigs in the last few weeks. How could I report something I didn't see?"

Cattle and pigs at all six infected locations in Britain were slaughtered on Friday.

Agriculture Ministry staff were investigating a further 600 farms which had also supplied livestock to the slaughter house at little Warley, southeast England, where FMD was first discovered earlier this week.

Wherever the disease is suspected, signs have been put up ordering anyone but essential workers to stay away.

Workers coming or going have been ordered to spray themselves and their vehicles with disinfectant.

In other measures, postmen have been asked to leave letters at farm gates, and some horseracing meetings have been cancelled.

The international fallout from the disease outbreak gathered pace as Thailand and Romania joined the list of countries outside the EU who had banned pork and live animal imports from Britain.

Poland, Russia and Singapore have already imposed their own bans.

The European Commission has already imposed an export ban on British meat and live animals, which it expects to remain in place for several weeks.

European Union governments were taking extra measures of the own, including cancelling agricultural markets to limit contact between herds and examining livestock which arrived from Britain in the last three weeks.

Ireland on Friday called up 300 troops to help police patrol its 240-mile (386-kilometer) border with Northern Ireland to keep out meat and livestock.

(IRNA)