US Secretary of State Hillary Clinton will today hold talks with Northern Ireland's political leaders in Belfast as they broker an historic deal on sharing responsibility for the region's justice system.

Republicans and unionists have yet to finalise an agreement on devolving policing and justice powers from Westminster to the Stormont Assembly, but lengthy talks with Prime Minister Gordon Brown last week carved out a financial blueprint for the move.

The American delegation will today discuss its continued political and economic support for the Irish peace process when Mrs Clinton meets First Minister Peter Robinson and deputy First Minister Martin McGuinness.

The US Secretary is making her seventh visit to Northern Ireland since she first arrived as First Lady with her husband President Bill Clinton to famously boost the fledgling search for peace in the 1990s.

As she arrived in Belfast last night, she threw her weight behind the efforts of the British and Irish governments to secure the devolution of policing and justice powers to Stormont.

"The step of devolution for policing and justice is an absolutely essential milestone," Mrs Clinton said.

Sinn Fein has been pressing for movement on completing the devolution of the powers, but the Democratic Unionist Party (DUP) has said it will not agree to a deal until all issues are resolved to its satisfaction.

The unionist party has also, however, been accused of stalling the process in the face of hard-line voices opposed to a deal with republicans, though this has been denied by party leader Peter Robinson.

The DUP leader said policing and justice were life and death issues that required careful handling by politicians.

The St Andrews political agreement that led to the formation of the power-sharing administration at Stormont, which is dominated by the DUP and Sinn Fein, promised the devolution of the powers.

Sinn Fein and the DUP have been engaged in a long running dispute over the timing of the move, though in the Autumn of last year they agreed an outline plan to deliver devolution.

Mrs Clinton said: "Clearly there are questions and some apprehensions but I believe that due to the concerted effort of the British government, Irish government and support of friends like us in the US, that the parties understand this is a step they must take together.

"It will take the leaders of both communities working together to continue not only the devolution but then to make day-to-day governing a reality, and I'm confident that that is within reach."

Gordon Brown led exhaustive talks over recent weeks aimed at delivering a final deal on devolution.

Mr Robinson and Mr McGuinness emerged from late night talks in Downing Street at midnight on Thursday, with the Sinn Fein representative declaring a final financial plan had been agreed.

Mr Robinson claimed the government offer was an advance on earlier proposals to cover the Northern Ireland policing budgets and courts service budgets, as well as financial pressures caused by legacy issues from the Troubles.

But while Mr McGuinness said he will advise his party to accept the deal, Mr Robinson has said it will have to be carefully scrutinised and did not represent the end of the process.

The DUP cited other issues it wishes to see dealt with, including moves to secure community confidence for the ground-breaking move that would see the creation of a ministry of justice at Stormont.