The BBC's Northern Ireland Correspondent Tom Coulter: A deal could be imminent

Mr Blair is on his second visit to the province in a fortnight amid heightened speculation that an announcement of progress is imminent.

He is said to be prepared to stay as long as necessary to strike a deal and the government said there were signs of slow progress.

A Northern Ireland spokesman said: "We are moving forward, but it is slow. It is genuinely difficult - we are talking about crunch issues."

This is Tony Blair's 10th trip to the province this year

The prime minister is anxious to resolve the impasse in Northern Ireland's politics, brought about by arguments over the balance of the new bodies established in the Good Friday Agreement.

He had a series of talks with First Minister David Trimble and members of his Ulster Unionist Party, and deputy First Minister Seamus Mallon and the SDLP. He also had discussions with Sinn Fein.

One senior Ulster Unionist source said there was still dispute over three cross-border bodies - trade and investment, Irish language and EU programmes and the number of ministerial departments in the new assembly.

Ulster Unionist Dermot Nesbitt: "Some progress has been made"

The trade and investment issue may be the most difficult to resolve. The SDLP is pressing for it to be included in the cross-border bodies, but unionists say it should remain under the control of the assembly.

A leading unionist said their opposition was that making trade and investment the responsibility of a cross-border body would have the effect of "hoovering out the economic functions from the assembly".

Ulster Unionist leader David Trimble: "Realism is spreading"

Mr Trimble, the Ulster Unionist leader, said: "We've been having this discussion over the last week or two. I think we're probably getting closer to a resolution and I think that realism is spreading."

Another unionist source said: "We are surely grown up enough to get through this and I am confident that we will. If not this week, I am confident that it will be soon."

Sinn Fein President Gerry Adams said: "Both governments have to remain focused if progress is to be made. The UUP are blocking progress, that situation is untenable."

Northern Ireland Political Editor Stephen Grimason on why Tony Blair is making the trip

During Prime Minister's Questions on Wednesday afternoon, Mr Blair came under pressure from former Northern Ireland Office minister Michael Mates for not insisting on decommissioning as a pre-condition to other moves.

Mr Blair told the Commons: "I understand the concerns of people who see those that have committed appalling murders being released on licence - not being given an amnesty but being released on licence.

Tony Blair says the Omagh bombing strengthened his determination to press ahead

"However, it is important that we are to make sure that all the elements of the agreement are adhered to, including decommissioning, and that we hold to our part of the bargain."

In an historic speech to both houses of the Irish Parliament last week, Mr Blair appealed to both sides in Northern Ireland to reach consensus.

Mr Blair became the first UK Prime Minister to address the parliament since Irish independence.

Then, a sense of crisis overshadowed the negotiations in Stormont.

Mr Trimble and Mr Mallon shaking hands: Disagreements may have been resolved

Mr Mallon warned the entire peace process would collapse unless a deal was struck on the composition of the new institutions within days.

That deadline, like a number of others recently, passed without progress.

But Mr Mallon said on Wednesday he was "still confident that before the end of the week we will have a resolution to this matter".

Irish Prime Minister Bertie Ahern may also join Mr Blair for the latest round of top-level talks at Stormont.