Alex Maskey had hoped to become Belfast's first Sinn Fein lord mayor

The Alliance Party's decision was described as "disgraceful" by Mr Maskey.

He said: "It flies totally in the face of the democratic wishes of people in this city and ensures that the status quo of unionist domination at City Hall remains." he said.

"Alliance is totally contradicting itself by supporting the election of an anti-Agreement unionist and is lining-up with the UUP, the anti-Agreement DUP and people who align themselves with the loyalist paramilitaries who have been causing the instability on the streets of this city in recent days."

The leader of the Alliance Party on the council, David Alderdice, said it had expected trust-building both inside and outside City Hall.

"Yes, there has been some cooperation in City Hall committees, yet there is much progress to be made," he said.

The move opens the way for another candidate to become lord mayor - probably Jim Rodgers of the Ulster Unionist Party.

The current lord mayor is Sammy Wilson of the anti-Agreement Democratic Unionist Party.

BBC Northern Ireland's political correspondent Mark Simpson said unionists would be relieved that he would not be forced to hand on the chain of office to Alex Maskey.

As for Sinn Fein, they had high hopes of taking the top job and will now be furious, he said.

Earlier, Alliance suggested it may have been willing to support Sinn Fein.

However, the party said it wanted a number of assurances from Sinn Fein before it would agree to support Mr Maskey for lord mayor.

The Alliance Party announced its decision at a news conference at 1000 BST on Monday.

Increased vote

The top job at Belfast City Hall has been withheld from republicans despite a big increase in their share of the vote in the city over a number of years.

Sinn Fein emerged as the biggest on the council on 12 June, winning 14 seats in the local government election.

It is now the only major party not to have taken the lord mayor's position.

Last year, Mr Maskey missed out on the lord mayor's post when an Alliance councillor voted with the unionists.

For many years, unionists felt they had a monopoly in Belfast City Hall.

After the Anglo-Irish Agreement was signed in 1985, unionists in Belfast hung a banner saying "Belfast says No" on the front of the City Hall.

Belfast Council Election

Sinn Fein 14 (+1) UUP 11 (-2) DUP 10 (+3) SDLP 9 (+2) Alliance 3 (-3) Others 4 (-1)

For some time, republicans were banned from marching to the building, which lies in the centre of Belfast, although it was a frequent rallying point for unionist protests.

These incidents led to a perception that the civic building was not being fairly shared by both sides of the community.

The first SDLP lord mayor of the city, Alban Maginness, was elected in 1997.