British Prime Minister David Cameron left Northern Ireland on Friday after marathon talks aimed at shoring up the province's fractious unity government ended without a deal being struck.

Cameron was meeting with Irish counterpart Enda Kenny and the executive's five parties amid differences over welfare reform and a series of symbolically significant issues linked to Northern Ireland's troubled past, like the holding of parades.

But he left Stormont House near Belfast early Friday saying that a failure to reach agreement meant London would not release a £1 billion ($1.57 billion, 1.26 billion euros) package to bolster the ailing finances of Northern Ireland's government.

"We have made good progress overnight and today but a deal is not going to be possible today," he said.

The five parties are particularly divided over implementing Westminster-imposed welfare reforms in the province, and over structural reform of its government.

Belfast has already requested a £100 million emergency loan from London, and if a deal on welfare reform is not reached, it faces penalty fees of around £200 million.

Republican party Sinn Fein said it was "distinctly underwhelmed by [Cameron's] generosity.

"There was no credible financial package on offer to executive ministers to allow us to combat the austerity agenda that this government has been inflicting on us," said Deputy First Minister Martin McGuinness.

"Our job was to try and arrive at a financial package that would allow us to protect public service jobs and hospitals and keep teachers in schools — to provide the essential services our people deserve.

"Thus far we haven't got that. But we don't give up."

First Minister and Democratic Unionist Party (DUP) leader Peter Robinson said there was a "responsibility to get the job done."

Both Sinn Fein and their DUP loyalist rivals have said a deal must be reached by Christmas.