DUBLIN (AP) — The prime ministers of Britain and Ireland, David Cameron and Enda Kenny, will travel to Belfast later this week in hopes of forging an agreement to sustain Northern Ireland's fraying unity government.

Aides to both leaders confirmed they would arrive Thursday at Stormont, the government complex in east Belfast, amid increasing concern that the 7½-year-old coalition of British Protestants and Irish Catholics, a key peacemaking achievement, could collapse without a new compromise pact.

The two principal parties in Northern Ireland's five-party coalition, the Irish nationalists of Sinn Fein and the British unionists of the Democratic Unionist Party, remain at loggerheads on a growing list of security, economic and cultural matters. The negotiations, which began in September, face an informal Christmas Eve deadline.

Deputy First Minister Martin McGuinness of Sinn Fein told lawmakers Tuesday that the window for compromise is closing fast, with no chance of meaningful diplomacy in 2015 before the United Kingdom's next general election expected in May.

McGuinness, a former Irish Republican Army commander who has jointly led the unity government with Democratic Unionist leaders since 2007, said the imminent arrival of Cameron and Kenny offers "a very clear indicator that people recognize we are coming to the crunch in these talks." He said failure to agree a comprehensive agreement to sustain power-sharing before Christmas would be "held up to public ridicule."

Failure could mean a renewal of direct British rule from London, the system of government that prevailed in Northern Ireland from 1972 to 1999, when the first in a series of feud-prone coalitions was formed under the terms of the U.S.-brokered Good Friday peace pact. The current coalition was formed after the outlawed IRA renounced violence and disarmed in 2005 and the IRA-allied Sinn Fein formally recognized the legal authority of the Northern Ireland police in 2007.