Sinn Fein's Alex Maskey is set to become the first republican mayor of Belfast after the cross-community Alliance Party gave him their backing.

After meeting on Friday to consider its position, the Alliance Party decided its three city councillors would back Sinn Fein as it was now "part of the democratic process".

The news was welcomed by Maskey, who vowed to work with other councillors if eventually chosen as mayor.

The three Alliance councillors on Belfast city council will now back Maskey's bid to become first citizen when the decision is taken next week.

With the cross-community party holding the balance of power between nationalists and unionists in City Hall, their decision was crucial to the outcome of the vote.

Unionist parties have 25 out of the 51 city councillors, while the SDLP and Sinn Fein have a combined total of 23.

Announcing his party's decision at a press conference on Friday, the leader of the Alliance grouping on the council, David Alderdice, said it was a "difficult and soul-searching decision".

Defending his decision, Alderdice said that despite concerns over republicans' refusal to back the new Police Service of Northern Ireland and the alleged links to Colombian terrorists, Sinn Fein was regarded "for better or for worse" as part of the democratic process.

Alderdice pointed out that Sinn Fein are the largest party on Belfast council, have two seats in the Northern Ireland executive, and could overtake the SDLP in next May's assembly elections.

"The best way to end continued IRA activity is to consolidate the primacy of the democratic process.

"I believe that by doing this, we will be consolidating peace by wedding Sinn Fein even closer to the democratic process. Once again, Alliance is taking a risk for peace. We are doing what we believe is the right thing to do," he said.

The Alliance Party said it had sought the advice of Northern Ireland secretary, Dr John Reid, on the state of the IRA ceasefire, who confirmed it was "imperfect" but still holding.

Alderdice pointed out that last year the party refused to back Maskey's bid to become mayor because the IRA had failed to respond to public demands for decommissioning, but since then had twice moved to put weapons caches beyond use.

"That is something that has benefited the political process enormously. It was recognised worldwide as one of the most significant steps ever taken by the republican movement.

"It was late, and was less than satisfactory, but at least the process has been commenced," said the Alliance group leader.

The party was also said to have been impressed by Sinn Fein's "dignified detachment" during the Queen's recent visit to Northern Ireland.

But there were still concerns at republican involvement in illegal activities, both in Colombia and in street clashes in Belfast.

Anticipating unionist criticism, Alderdice noted that their leaders they had elected a loyalist councillor, Hugh Smyth of the Progressive Unionist Party, as lord mayor before there was an Ulster Volunteer Force ceasefire.

Maskey welcomed the Alliance's decision as "good news".

"I am not yet counting my chickens as there is still five days to go before the council vote but if I am elected, it will be a good day for Belfast.

"As first citizen, I will seek to work with everyone. I would like to say to Alliance that as mayor I will reward your trust," he pledged.