Prime Minister Gordon Brown and Taoiseach Brian Cowen arrived in Northern Ireland tonight to lead emergency talks aimed at saving Stormont's crisis-hit power-sharing government.

The dramatic intervention by the British and Irish leaders was announced earlier today after a last-ditch attempt by Sinn Fein and the Democratic Unionists to find agreement over the devolution of policing powers failed.

Amid fears that republicans could collapse the fragile institutions - forcing a snap assembly election - if the DUP do not agree to a swift transfer of law and order responsibilities from London, the two governments will meet both parties at Hillsborough Castle in Co Down.

Mr Brown and Mr Cowen decided to fly to the province after holding talks at Downing Street this afternoon.

"We believe that the problems that exist in devolving policing and justice are soluble problems," Mr Brown said.

"We believe it is right for Northern Ireland to move forward in this way and we believe that together we can assist in the completion of these talks."

The two premiers arrived in Hillsborough at 5pm in an 11-vehicle cavalcade escorted by a fleet of police outriders.

Their arrival came hours after a crunch meeting between DUP leader Peter Robinson and Sinn Fein Deputy First Minister Martin McGuinness in Parliament Buildings at Stormont.

The exchange lasted little more than half an hour and ended without resolution.

Earlier, Mr McGuinness accused the DUP of failing to fulfil its obligations in regard to policing and justice.

The senior republican claimed that, while his party had backed new policing structures after the 2006 St Andrews Agreement which paved the way for power-sharing, the DUP had yet to agree to a key element of that accord - namely devolving law and order powers to the Stormont Executive.

The region's largest unionist party has claimed there is still not sufficient community confidence to justify the move.

Specifically, the DUP has demanded changes to the current process of managing contentious parades in Northern Ireland before the transfer of responsibilities from Westminster can go ahead.

But Mr McGuinness said: "Within three months of the St Andrews Agreement we in Sinn Fein moved forward decisively on the issue of policing, took what was considered to be an historic and monumental decision.

"And we did that within three months of St Andrews... to ensure that these institutions would work.

"Three years on, three years on, we are waiting for the DUP to deliver and honour their commitments, that all of us were supposed to have signed up to under the terms of an agreement that was presided over by the Irish government and the British government."

But acting DUP First Minister Arlene Foster, who has temporarily taken on Mr Robinson's official duties while he deals with the fallout from the sex and money scandal involving his wife Iris, said her party remains committed to finding an agreed way forward.

"We want to find a resolution to the difficulties we find ourselves in at this present moment in time," she said.

The minister also downplayed talk of a full-blown crisis.

"I think we need to all calm down, look at what the outstanding issues are and work through them," she said.

Mr Brown said the visit had been planned in conversations between the two leaders yesterday.

"While I recognise that there are difficult issues, we believe that these issues can be overcome," he said.

"So we will together go to Northern Ireland and talk to Mr Robinson and Mr McGuinness and talk to other parties in Northern Ireland and we believe there is a chance that progress will be made."

Mr Cowen said the premiers believed their visit "should help bring a conclusion to the devolution issues".

Asked whether they could set a date, Mr Cowen said: "There is no doubt that we need to resolve this matter in a way that would assure that devolution of policing and justice would take place in a specified period.

"We believe that with goodwill and determination and good faith on all sides it should be possible. We believe the outstanding issues are resolvable."

Posed the same question, Mr Brown replied: "We are going to be talking to people this afternoon about all the issues and I believe that the end product will be that devolution of policing and justice will take place."

Sinn Fein president Gerry Adams and Mr McGuinness briefed their assembly members at Stormont ahead of the meeting with the two leaders.

Sinn Fein and DUP negotiators arrived soon after the two premiers for what was expected to be sensitive late-night talks.

Outside Hillsborough Castle, Irish Foreign Affairs Minister Micheal Martin underlined the two governments' commitment to sealing a deal over the coming days.

"It's our view given the seriousness of the situation, and there is no point in saying otherwise, that both the Taoiseach and the Prime Minister were prepared to give their time to come here to assist the parties to endeavour to bring this to a resolution," he said.