Elements of the Democratic Unionist Party (DUP) remain opposed to sharing power with Catholics, Sinn Féin president Gerry Adams controversially claimed tonight.
The republican leader told a party conference in Belfast that sections of the DUP also used abusive terms to reject nationalist plans to promote the Irish language.
He warned that the unionist party had threatened the power-sharing institutions by failing to agree a deal with Sinn Féin on the issues dividing the two parties, which include the proposed transfer of policing and justice powers from Westminster to Stormont.
Mr Adams confirmed tonight that the party's existing MEP Bairbre de Brun would again fight the seat in next year's elections to the European Parliament.
He praised the work of Ms de Brun, but his speech focused on the challenges facing the Northern Executive, which has failed to meet since June as a result of the Sinn Féin/DUP stand-off.
He also dismissed claims the crisis centred on his party's blocking of Executive meetings.
"It lies in the DUP's refusal to work the Executive as a partnership and power-sharing government," said Mr Adams.
"And it lies in the desire of some DUP representatives who want to run the institutions in the same way unionism used to run the North - in their interests solely, even though the leadership knows this is not sustainable."
The DUP made the ground-breaking decision to enter government with Sinn Féin in May 2007 under the party's then leader Ian Paisley - who retired in June this year to be replaced by Peter Robinson.
Since then republicans have had an increasingly frosty relationship with their political partners as time passes without a deal on devolving justice powers.
Tonight Mr Adams launched a further strongly-worded attack on his political opponents.
"It is obvious that there are elements with the DUP who do not agree with power sharing and partnership as a political model or a practical politics," said Mr Adams.
"In addition, there are clearly elements of the DUP who really don't want to have a Catholic about the place. They are opposed to power sharing in any form.
"And some of them clearly believe that by stalling and delaying they can hollow out the Good Friday and St Andrews Agreements.
"As a result of this opposition the DUP has been retreating from its obligations under the St Andrews Agreement."
He added: "They have failed to embrace partnership government, they have run away from policing and justice obligations, they seek the retention of an outdated class based education system, and have sought to undermine the rights and entitlements of Irish speakers.
"And all of this is wrapped in the most abusive and offensive language."
The St Andrews Agreement of 2006 set May of this year as a target date for the transfer, but the DUP has said it will only move when it is ready and recently rejected calls from the British prime minister Gordon Brown to set a date for the handover.
Mr Adams said: "In effect the position adopted by the DUP since June is a challenge to all of the parties and in particular to the two governments."
The Sinn Fein President praised the work of Bairbre de Brun as an MEP and said his party was looking forward to the European campaign.
"The election north and south will be a major challenge for Sinn Féin and we will have to maximise our efforts to ensure a good result," he said.
"I believe that with Bairbre's record of exemplary work and a good organisational campaign by Sinn Féin that we can look forward to a successful election campaign."
He said his party was the only group standing European election candidates across Ireland north and south.