Sinn Fein's John Finucane has accused the DUP of "putting their own narrow interests" ahead of Northern Ireland following the breakdown of Brexit talks in Brussels.
Mr Finucane, whose solicitor father Pat was murdered by loyalist paramilitaries, was speaking at a white line protest in west Belfast days after the DUP forced Prime Minister Theresa May to pull the plug on the deal the government had agreed with the EU.
As talks between Mrs May's government and EU officials continue, dozens of protesters held placards demanding that there should be no border between Northern Ireland and the Republic after Brexit.
Addressing the crowd on the Falls Road, Mr Finucane said: "Even by the unpredictable nature of politics recently, what we have witnessed this week has been breathtaking, in the contempt that has been shown.
"This week the British Government finally made proposals to the President of the European Commission on Monday.
"What we all witnessed in response to this was the DUP vetoing this agreement in their own narrow, sectoral interest.
"Not only does this continue to highlight the unhealthy relationship between the Tory government and the DUP, but they are putting their own narrow self interest before people's lives and livelihoods."
Sinn Fein also unveiled a mural following last night's protest that called for Northern Ireland to be granted a "special status".
Mr Finucane continued: "The solution to Britain's Brexit crisis in Ireland is clear. The north of Ireland should have designated special status within the EU ensuring that we remain within the Customs Union and the Single Market.
"That is the only guarantee of stability and certainty, ensuring delivery of the full protection of the Good Friday Agreement."