The Garda tightened security along the Border last night after the North's Agriculture Minister, Ms Brid Rodgers, confirmed that 21 sheep on a south Armagh farm had foot-and-mouth disease.
Extra soldiers will be moved to the Border today while Civil Defence units will also be mobilised, on foot of decisions taken at last night's two-hour Cabinet meeting.
Gardai began to seal off all but 30 of the roads crossing the Border in an attempt to stem any further movement of livestock into the Republic.
A Garda spokesman, said that some 500 gardai had been posted to the Border by yesterday evening.
About half the road crossings between Northern Ireland and the Republic had checkpoints by yesterday, according to the Garda.
However, roads were still open yesterday afternoon in the so-called exclusion zone around the affected farm in Armagh.
About 200 soldiers from the Western and Eastern Brigades were on Border duty, but only about a quarter of these were on patrol at any given time.
A decision on the number of extra troops to be deployed will be taken today when the special taskforce set up to deal with the crisis meets.
The reinforcements will be used at static checkpoints, so that gardai will be freed up for mobile patrols. Leaders of the Civil Defence have also been asked to attend today's meeting. Extra staff will also be found within the Department of Agriculture to man checkpoints and check for animal movements.
Meanwhile, ministers voiced concern at headlines yesterday in newspapers other than The Irish Times which described foot and mouth as being "here" even though the suspected outbreak was north of the border. They said the headlines had led a number of countries, particularly Argentina, to voice doubts about taking future Irish exports. The Government may now bring in all newspaper and broadcasting editors for a special briefing.
Before the Cabinet meeting, the Government's handling of the crisis was sharply criticised by the Opposition. "The response has been wholly inadequate," the Labour TD, Mr Brendan Howlin, said.
Returning from an official visit to Wales, the Taoiseach told reporters that the Government had begun to take action last week "as soon as we heard about the United Kingdom, before even the EU did anything."
"It is a huge effort effectively to cut off an island", he said.