I recognise how significant this decision is for republicans Mo Mowlam, Northern Ireland Secretary

The agreement came at the party's annual conference, which included about 30 IRA prisoners granted special leave to vote.

The British and Irish governments welcomed the decision to formally approve the peace agreement signed at Stormont in April to create the Northern Ireland Assembly and new cross-border institutions.

The Irish Prime Minister, Bertie Ahern, said he now looked forward to an overwhelming 'yes' vote in referendums on the deal later this month.

The British government praised the Sinn Fein leader, Gerry Adams, saying the decision marked a final realisation that violence did not pay.

The Northern Ireland Secretary, Mo Mowlam, expressed her delight at the outcome.

"I recognise how significant this decision is for republicans and pay tribute to the leadership of Gerry Adams in bringing his party to support the agreement, north and south of the border," she said.

In what she described as an "exceptional decision", the IRA's commanding officer in the Maze Prison Patrick Wilson was among the 30 republican inmates freed for the conference in an effort to bring about a "Yes" vote.

Sinn Fein also voted to amend its constitution to allow members to sit in a new Northern Ireland Assembly after Mr Adams told his members they had a real chance to influence the strategy of the party and the way towards a united Ireland.

Martin McGuinness, one of Sinn Fein's UK MPs, told the BBC he was optimistic about achieving a "Yes" vote in the referendum due to be held on 22 May.

"I think there are concerns naturally among a small section of the Sinn Fein membership, but I have to say I think the mood all over the island is that moving into the assembly to further our republican objectives towards our ultimate goal of a united Ireland is at this moment in time the sensible thing to do," he said.

	E-mail this story to a friend