Two extra battalions - about 1,000 men - were preparing to leave Britain, possibly by the end of the week. There will then be 13 battalions in the province - some 18,500 soldiers - the highest number since 1982 and more than before the IRA called its ceasefire in 1994. One Unionist leader warned: "There will be bonfires across Ulster."
Late last night, however, there was a dispute between London and Belfast about when the soldiers would be sent in. An Army spokesman in the province said he hoped they would be in place by the end of the week. But the Ministry of Defence in London insisted no decisions had been made on the exact timing of the deployments. A spokesman said: "We will see how the situation develops."
The confrontation at the churchyard at Drumcree, where Orangemen and police faced each other across a barricade of concrete and barbed wire, could prove to be the beginning of a disaster, with the potential for reducing the peace process to ruins and putting the survival of John Major's government at risk.
As the tension heightened, the Prime Minister gave his total backing to the decision by Sir Hugh Annesley, the Chief Constable of the Royal Ulster Constabulary, to halt the Orangemen's march at Drumcree.
Ian Paisley, leader of the Democratic Unionists, David Trimble, leader of the Ulster Unionists, and Robert McCartney, the Independent Unionist MP, held an emergency meeting with Mr Major to press for a climb-down by the security forces.
They warned him that there could be up to 80,000 Orangemen at Portadown on Friday. "It is a powder keg which could only by resolved when a decision is taken by the Prime Minister," Mr Paisley said. "There will be civil commotion. This is serious and it is getting more serious."
But Mr Major insisted on backing the operational decisions of the RUC. In the Commons, he condemned the violence as "indefensible" and warned that it could set back the search for peace
However, the cross-party talks have become a side-issue in the confrontation leading up to the marching day of 12 July, the anniversary of the Battle of the Boyne.
The eruption early yesterday, which is likely to cost the province's economy and tourist industry millions of pounds, saw some of Belfast's worst loyalist violence for years.
Two Catholic schools were damaged in fires and four Catholic families were forced to leave their homes in the Old Park area after intimidation by gangs of loyalists. Maria Darragh, one of the Catholic residents left at Torrens Drive, said she would also have to leave the area. "In the end, the fact is that I am a Catholic living in a Protestant area. We are just going to have to go."
The intimidation was attacked as "ethnic cleansing" by Paddy Ashdown, the Liberal Democrat leader.
Labour's spokesman for Northern Ireland, Mo Mowlam, made a surprise visit to the scene in Portadown last night. Mr Breandan MacCionnaith of the Garvaghy Road Residents' Association, from the Nationalist area where the Orangemen are barred from marching, said the MP had visited them at their request.
He said: "She came at our invitation to listen to what we have to say. We are the victims in this but in some quarters in Britain we are being portrayed as the aggressors. She was sympathetic and heard what we had to say. I hope that she is going to condemn the Unionist violence and condemn Dr Paisley and Mr Trimble over what is going on here."
Some MPs believe Unionist leaders are fanning the flames. Mr Trimble has appeared on the Orangemen's front line, although he has been appealing for restraint.
Confrontation with the Unionist MPs on whom Mr Major may have to depend increased the threat of defeat in the Commons. His one-seat majority could be put to the test before the end of the month.