Taoiseach Enda Kenny and British prime minister David Cameron were left in no doubt by the Northern parties that achieving a deal to stabilise the Stormont institutions remains difficult and complex, according to senior sources.

As negotiations continued at Stormont, well-placed talks insiders said that early optimism was turning to a cold understanding that it remains problematic whether a deal can be struck between the governments and the parties.

After arriving at Stormont House, Mr Kenny and Mr Cameron circulated a joint working paper to the five parties and then started engaging in a series of one-to-one meetings with party leaders and their other senior negotiators. Talks are concentrating on financial issues, the past, parades and flags and restructuring Stormont.

“The early enthusiasm that a deal could be done quickly turned to a realisation that the issues are extremely complex and will take time,” said one senior source. “There is definitely no immediate quick fix.”

Sources said it was too early to say when and if a resolution could be achieved with some saying that whatever progress is achieved in these talks may have to be “banked” with all-party talks continuing next week to determine if final issues can be resolved.

Dublin’s focus was on “seeking maximum possible implementation of the Good Friday agreement, firm commitments on dealing with the past on the basis of the Haass proposals and expanding the role and remit of the North-South institutions”, added a senior source.

Nonetheless the talks were to continue at Stormont to determine if agreement could be achieved by Friday evening.

Mr Kenny was accompanied in the talks by Tánaiste Joan Burton, Minister for Foreign Affairs Charlie Flanagan and junior foreign minister Sean Sherlock. Mr Cameron was joined by Northern Secretary Theresa Villiers, who warned ahead of the negotiations against the parties expecting a major financial package from the British government.

This was viewed as an attempt to dampen demands by the five Northern parties - the DUP, Sinn Féin, the SDLP, the Ulster Unionist Party and Alliance - for a significant British financial package to offset budget cuts of £1.5 billion over the next five years and change to the North's welfare system.

The parties countered by insisting that first and foremost a financial dividend for Northern Ireland was crucial to any prospect of a deal. Sinn Féin upped the ante considerably by demanding additional British funding of at least £1 billion, according to talks sources.

Mr Cameron said he was prepared to discuss finances and budgets but told the parties that he was restricted in what he could deliver.

Sinn Féin Deputy First Minister Martin McGuinness insisted that Northern Ireland was a special case as it was a society “emerging from conflict”. “This place here is different. This is not the north of England. This is not London. This isn’t Scotland, and this isn’t Wales,” he said.

DUP negotiator Jeffrey Donaldson said the alternative to a financial deal and agreement on the other key issues was that the Northern Executive and Assembly “comes crashing down and that we go back to direct rule...we end up with water charges and we end up households in Northern Ireland paying higher taxes and having a lower standard of living”.

Before entering the talks, Mr Kenny said progress already had been made in the talks and that the “environment was very good” although that was not to underestimate “the challenges that we face here”.

The British prime minister said he was “always an optimist” and this was his position about the talks. “I think everyone in Northern Ireland wants the same thing; an economy that grows; politics that work and a society that gets stronger,” he said.

Mr Cameron said the politicians in the negotiating room had to demonstrate that they could resolve a range of issues - “over the budget, over finance, over flags, parades and the past”.

“The people outside that room - they are the people who matter and they want to see their politicians deliver,” he said. “I hope agreement can be reached and that is why I am here.”