A serious split has opened up in the top ranks of the Irish Republican Army (IRA), posing a threat to the Northern Ireland peace process, British security officials say.
The British and Irish governments fear the schism will put pressure on the renewed cease-fire called in July, which has made possible all-party talks that include representatives of Sinn Fein, the IRA's political wing.
British sources say at least two key members of the IRA's top leadership have resigned from the organization in recent weeks.
The IRA leaders claimed that by signing the so-called Mitchell principles on nonviolence, Sinn Fein president Gerry Adams betrayed the cause of militant Irish republicanism, the sources said.
By agreeing to the Mitchell principles, which call for "total disarmament of all paramilitary organizations," Mr. Adams and chief Sinn Fein negotiator Martin McGuinness were able to gain admission to the Belfast peace talks.
David McKittrick, a leading analyst of Northern Ireland affairs, says the row "poses fundamental questions about the control which Adams and McGuinness have over the republican movement."
"This breach represents the most serious and most public rift within the organization's ranks for well over a decade," Mr. McKittrick says.
The identity of the IRA's top leadership, which in the past has planned numerous terrorist attacks in Britain and mainland Europe, is a closely guarded secret. But reliable British security sources have confirmed that the two senior officials had quit.
The sources said one of them was a member of the organization's seven-person "army council," and the other was responsible for controlling and allocating IRA weapons and explosives used in terrorist attacks.
Further evidence of turmoil in the upper reaches of the IRA came over the weekend with news that 12 Sinn Fein members in County Louth had announced they could no longer back the leadership of Adams and Mr. McGuinness.
Official confirmation of "difficulties" over IRA and Sinn Fein policy came last Friday from Mitchel McLauchlin, chairman of Sinn Fein. "The peace process itself, this collaboration with all the political forces on the island, isn't seen to be delivering the goods, and that's going to cause problems for us all," Mr. McLauchlin said in a statement.
Underlying concern being voiced privately by the British and Irish governments is the possibility that the dissident IRA officials may join an existing breakaway faction or create a radical movement of their own.
Since the peace talks got under way in September, several bomb attacks have been reported in Northern Ireland and the Irish Republic.
British security sources say they appeared to be the work of a group calling itself the Continuity IRA. McKittrick says there are indications that explosives used by this group may have been supplied by lower-ranking IRA members.
"In at least one of these incidents the bombers used Semtex, a plastic explosive which has in the past been the almost exclusive preserve of the IRA," McKittrick wrote Saturday in the British newspaper The Independent.
There are few details about the arguments that led to the IRA split, but Toby Harnden, an analyst of Irish politics, says a meeting was held last month of the IRA's 50-strong general army convention, the organization's supreme decisionmaking body, soon after Adams signed on to the Mitchell principles.
Mr. Harnden says some 20 members of the convention attacked the move and called for an end to the cease-fire.
When a vote went against them, several of the dissenters indicated they would leave the IRA rather than support the Adams-McGuinness policy.
The "somber assessment" by British security officials, Harnden says, is that "the desire to maintain unity would probably lead to the end of the cease-fire before the middle of next year."
One possible cause for hope would be significant progress at the all-party talks, but so far there has been little sign of even a partial meeting of minds between Adams and McGuinness on the one hand, and Unionist politicians on the other.
David Trimble, leader of the Ulster Unionist Party, Northern Ireland's largest pro-British party, on Friday described the IRA resignations as "choreographed divisions" within the republican movement.
"The IRA has not changed its character. The present cease-fire cannot be regarded as anything other than a tactical maneuver," Mr. Trimble said.