The Stormont talks appeared to be close to crisis last night amid indications that the Ulster Unionist Party had rejected the package worked out between the party leaders over the past 10 weeks.
While sources close to the UUP leadership still insisted all was not lost, Mr Gerry Adams said Sinn Fein had been told that the unionists had said "no" to the deal. The talks will resume this morning.
The Northern Ireland Secretary, Mr Peter Mandelson, spearheaded an intense effort during the evening to persuade the unionists to accept the package on offer.
The deal included statements of peaceful intent from Sinn Fein and the IRA but failed to guarantee short-term decommissioning of paramilitary weapons.
Mr Adams told a brief news conference shortly before 10 p.m.: "Sinn Fein is deeply disappointed at the turn of events today.
"We had hoped to have successfully concluded the review by now. We have been told that the Ulster Unionist Party have said `No'. I am asking everyone to reflect on this and on the seriousness of it."
There were sharply conflicting accounts emerging from meetings held by the UUP Assembly party at Parliament Buildings throughout the day.
First, a report received widespread circulation that the deal had been rejected by the Assembly members in a vote taken early in the day, with figures of 14 against and 13 in favour of the package being quoted by some elements of the news media.
However, The Irish Times has learned that a majority of UUP Assembly members in fact supported Mr Trimble's proposal to refer the deal to a special meeting of the Ulster Unionist Council.
Although no formal head count was conducted, sources indicated a likely margin of 19 to seven in Mr Trimble's favour.
However, it appears that Mr Trimble's calculation that he is unable to proceed with the deal is based on the quality of the opposition within the Assembly party.
This opposition, it is understood, was led by his deputy leader, Mr John Taylor.
The loss of five Assembly members would be enough to give the anti-agreement unionist bloc in the Assembly the requisite 60 per cent share of the unionist vote necessary to block Assembly business.
Mr Danny Kennedy (Newry and Armagh) and Mr Fred Cobain (North Belfast) are believed to be among those firmly opposed to the deal.
The realisation that short-term decommissioning was not on offer from the IRA reportedly came as a shock to some members of the UUP Assembly team. Their deliberations were held in private.
As the talks closed down last night, a UUP spokesman said: "It would be wrong to write this off. We will be back here tomorrow. "The party leader is determined to try and make this work."
IRA men mentioned as interlocutors on arms; DUP leader calls for