Blair told lawmakers in the House of Commons that the province's major Protestant party, the Ulster Unionists, needed to know more about the IRA's move Tuesday — confirmed by an official observer — to "decommission" more of its arsenal.
The IRA move had been designed to rebuild Protestant support for resuming cooperation with the IRA-linked Sinn Fein party, but Ulster Unionist chief David Trimble rejected it because the IRA refused to permit any announcement of the weapons, the quantity or the means of putting them out of use.
Protestants "need to be sure that what is being said is a substantial act of (arms) decommissioning is indeed a substantial act of decommissioning," said Blair, who called the impasse "deeply frustrating."
As Blair spoke, negotiators from Sinn Fein and the Ulster Unionists met at a castle near Belfast to discuss whether they could resolve their arguments before an election Nov. 26 for the province's idle legislature.
"This issue has to be settled between us," said Mitchel McLaughlin, chairman of Sinn Fein.
The election, which Blair announced Tuesday after months of delays, would determine whether power-sharing has a chance of revival.
Protestant opinion has hardened against sharing power with Sinn Fein unless the IRA disarms fully and ceases a list of hostile activities — the issue that triggered the collapse of power-sharing last October.
Blair praised Tuesday's statements by the IRA and Sinn Fein leader Gerry Adams. Taken together, Blair said the Sinn Fein-IRA movement had accepted in public for the first time that Northern Ireland's Good Friday agreement of 1998 — if enacted fully — "means an end to the conflict in Northern Ireland."
But Blair called the IRA's insistence on keeping disarmament details secret "an unsatisfactory situation." He noted he had been given a much more detailed briefing of the IRA's weapons offerings by John de Chastelain, the retired Canadian general overseeing disarmament, and felt certain that Protestants would be impressed by what happened "if they knew the full details."
De Chastelain confirmed Tuesday that the IRA had allowed him to inventory and "decommission" a cache of automatic rifles, explosives and other weapons on Tuesday.
But Trimble — whose party is essential in reviving power-sharing — lambasted the IRA for keeping details vague.
Irish Prime Minister Bertie Ahern, who also traveled Tuesday to Northern Ireland for what he hoped was to be a day of breakthroughs, said that he had been worried that the IRA would insist on too much secrecy.
"The problem all along was the one person that we don't deal with is the IRA representative who deals with the issue of decommissioning. We have no contact with that person," Ahern told lawmakers Wednesday in Dublin.
Adams said Wednesday he hadn't received an adequate explanation from the Ulster Unionists about why they had rejected the IRA arms move. He said he expected Trimble to issue a statement, as previously agreed during negotiations, committing the Ulster Unionists to revive power-sharing if they receive sufficient Protestant support in the Nov. 26 vote.
If hard-liners led by Ian Paisley win a majority of seats on the Protestant side of the legislature, they could block formation of any administration. Paisley insists he would never vote to install Sinn Fein into any government post in Northern Ireland.
Trimble's support on the Protestant side has steadily ebbed since he agreed in 1999 to lead a 12-member Cabinet that included two Sinn Fein members. The coalition suffered repeated crises over the IRA's slowness to disarm and continuing hostile activities.
Power-sharing collapsed in October 2002 after police said they had uncovered evidence that Sinn Fein's top legislative aide was involved in an IRA operation to gather intelligence on potential targets.