The Ulster Unionists said last night that because of the stand-off between Orange Order supporters and the Royal Ulster Constabulary at Drumcree, near Portadown, Co Armagh, they would not be fielding a team at the Stormont talks.
The Ulster Unionist leader, David Trimble, pledged: "We are not closing the doors by any means." His party colleague, the Rev Martin Smyth, a Grand Master of the Orange Order, added: "I don't believe we should be having the requiem mass for them [the peace talks] at this stage."
Democratic Unionist Party leader, Rev Ian Paisley, told crowds of protesters at Drumcree that he and Mr Trimble would meet the Prime Minister, John Major, tomorrow. A Downing Street spokesman said: "A request has been made to see the Prime Minister, which is under consideration."
The boycott of today's talks was announced after a day of ugly scenes as Orangemen stepped up their protest at not being allowed to march through a Catholic area in Drumcree.
Demonstrators closed the international airport at Aldergrove, just outside Belfast, by blocking its access roads.
Roads were also blocked at Bangor, Ballymena, Londonderry, Garvagh, Coleraine and throughout Belfast. The RUC was yesterday advising motorists not to travel unless the journey was absolutely necessary.
Last night, up to 2,000 police officers faced several thousand angry loyalists in Co Armagh.
By nightfall the arrest tally had reached 22, mainly for public order offences. A 19-year-old masked man was arrested on the outskirts of Portadown carrying a crossbow as he attempted to hijack a lorry. A crate of petrol bombs was found nearby.
Mr Trimble accused officers of "deliberate provocation" after they fired plastic bullets at loyalists as soldiers set up a concrete and barbed wire barricade on the Drumcree Road leading into the Catholic area of Garvaghy Road.
Numerous parades across the province took place in sympathy with the Orangemen at Drumcree, including one, accompanied by bands, through the centre of Portadown.
Loyalists hope that at least 300,000 people will show their solidarity in a protest in Drumcree on 12 July, the anniversary of the Battle of the Boyne.
Last night, the numbers of people at the site of the barred march at Drumcree swelled assympathisers flooded in from all over the province.
The district Orange leader, Harold Gracey, warned: "We have our contingency plans. I think the province is going to erupt," he added. "This is not just the siege of Drumcree but the siege of Ulster."
Within the 5,000-strong Catholic community, the feeling was of "resolute determination" not to allow the Orangemen have their way again.
Breandan MacCionnaith of the Garvaghy Road Residents Association said: "We have had two days of violence and there is no sign of the Unionist leaders trying to control their people."
Another Catholic leader warned that it seemed too late for any compromises to be made. "Things have gone too far," he said.
Last night the focal point of the stand-off was generally peaceful. Orange Order members who had been at the roadblock all day were replaced by members of lodges from different parts of the province as darkness fell. The demonstrators maintained a constant drumbeat.
The RUC said up to 70 roads in the province had been blocked by demonstrators.
Police said it was too early to link the murder of a Catholic man near Lurgan, a few miles from Portadown, with the sectarian disturbances in the town.
Part-time taxi-driver Michael McGoldrick, 31, from Lurgan, was found with head injuries yesterday morning.