Tony Blair has welcomed Sinn Fein's vote in support of the Police Service of Northern Ireland (PSNI) as a "historic decision".
Irish prime minister Bertie Ahern also praised last night's "landmark" decision by the party's Ard Fheis to end its 86-year opposition to policing in the region.
The move clears a major obstacle in the way of the restoration of power-sharing government between Sinn Fein and the Democratic Unionist Party (DUP) at Stormont, which, under the terms of the St Andrews agreement, could take place in March.
However, the DUP is still sceptical, with leader Ian Paisley warning: "Only with real delivery can the way be cleared for a full return to democracy, and the facing up to the everyday needs and requirements of the people of Northern Ireland."
Party members voted by 90 per cent to back the Sinn Fein leadership's motion to support the PSNI and the rule of law, and encourage the nationalist community to cooperate with the criminal justice system.
Speaking after the vote, party president Gerry Adams said: "The decision we have taken today is truly historic. What its significance will be, will be how we use this decision to move our struggle forward.
"Today you have created the potential to change the political landscape on this island forever."
Mr Adams appealed to unionists to accept the "historic compromise", looking to "the promise and hope of the peace process. to deliver stability, progress and prosperity for all our people".
He also called on hardline republicans who left Sinn Fein anticipating last night's decision to meet him and explain "any alternative strategy they want to put forward".
Mr Blair and Mr Ahern will meet tomorrow to discuss the situation, as the latest report from the Independent Monitoring Commission (IMC) is expected to confirm the IRA is still upholding its promise in July 2005 to renounce violence and criminality.
The prime minister said the next few weeks - which will see the assembly dissolved at midnight tomorrow to prepare for new elections on March 7th - would as "important as the negotiation of original Good Friday agreement".
"We will determine whether we have a basis for the future in Northern Ireland that allows us both to have power-sharing between unionists and republicans and nationalists, really on a solid basis for the first time ever," he told BBC One's Politics Show.
"And have a situation where everybody in Northern Ireland supports, and supports properly the police, the courts and the criminal justice system, and a what a fantastic thing that would be instead of waking up - as we used to years ago - to violence and terrorism in Northern Ireland, we have the prospect of peace."
If everything goes as planned, the elections should deliver a new assembly and a new power-sharing government would be formed at Stormont on March 26th.
To read more responses to Sinn Fein's decision visit our issue of the day.