Political leaders in Belfast and Dublin have condemned the Democratic Unionist party (DUP) for paralysing the Stormont assembly and executive in a dramatic escalation of the party’s campaign against the Northern Ireland protocol. Sinn Féin and other parties in Northern Ireland described the move as “shameful” and “disgraceful” and said it treated voters with contempt. The row turned what was supposed to be the inaugural day of the assembly into a farce in which newly elected representatives signed the roll at Stormont – and became eligible to collect salaries – but were left without duties, functions or power. A DUP abstention prevented the assembly electing a speaker and elicited angry exchanges in the chamber. Alex Maskey, the outgoing speaker, will remain in a caretaker role, as will former ministers. Michelle O’Neill, Sinn Féin’s deputy leader and the region’s putative first minister, accused the DUP of denying democracy. She told the chamber she was ready to “take on the leadership of the Northern Ireland executive as a first minister for all”. It was believed to be the first time she had publicly used the term Northern Ireland. Sinn Féin usually refers to the region as “the North”. O’Neill later told reporters Boris Johnson, the prime minister, planned to visit the region on Monday. “I intend to put it to him directly that he needs to stop pandering to the DUP,” she said. The DUP had announced earlier on Friday it would pull the plug on the legislature as well as the executive. Under power-sharing rules the assembly and executive cannot function without the DUP. The decision plunged Northern Ireland into political crisis a week after a historic assembly election in which Sinn Féin overtook the DUP as the biggest party. It is a message to Downing Street and the EU that the DUP is willing to create a destabilising vacuum in Northern Ireland to secure changes to the protocol, which puts post-Brexit checks on goods entering the region from Great Britain. Sir Jeffrey Donaldson, the DUP leader, said the prime minister must “outline what he intends to do”. The protocol violated the principle of consent – which requires support from nationalists and unionists – on which rested the Good Friday agreement, said Donaldson. He hinted there would be no swift resolution to the impasse: “I have both patience and resolve in equal measure to see the Irish Sea border removed, and stable as well as sustainable devolution restored.” DUP strategists hope the crisis will embolden Johnson and Liz Truss, the foreign secretary, and strengthen their hand in a showdown with the European Commission. The mothballing of Stormont means civil servants and ministers from the outgoing administration, with reduced powers, will run Northern Ireland in what has been termed a “zombified” state. They cannot make important decisions or launch new initiatives. During the election the DUP had vowed to block the formation of an executive but not the assembly. “This is disgraceful,” said Colum Eastwood, the Social Democratic and Labour party (SDLP) leader. “The DUP have no mandate for this as they told everyone during the election debates that the assembly would continue.” Naomi Long, the leader of the Alliance party, the third-biggest party after Sinn Féin and the DUP, also excoriated the DUP and said its assembly members should not be allowed to claim salaries while Stormont was paralysed. “If the DUP don’t want to do the job, they could not sign in and forfeit their salaries. But they won’t, of course. They’ll just stop every other MLA from doing all of the job they were elected to do.” Neale Richmond, a Fine Gael member of the Irish parliament in Dublin, said the move would not help anyone in Ireland, north or south of the border. “Constantly saying no is not feasible.” DUP strategists say the party had to pull the plug on Stormont to exert leverage on Downing Street and Brussels. The boycott may also shore up support among unionists who during the election defected from the DUP to its more radical rival, the Traditional Unionist Voice. Jamie Bryson, a leader of anti-protocol rallies, congratulated Donaldson. “Well done sir. To put it simply; the cry is No Surrender!” he tweeted. The boycott will dismay business leaders and unionists who have called for pragmatic solutions to managing the protocol. On Thursday, the Royal College of Nursing, the British Medical Association Northern Ireland, the Royal College of Surgeons of England, the Royal College of Emergency Medicine and the Royal College of GPs warned that failure to form an executive would endanger patients’ lives. “Our health service is on the verge of collapse,” they said a joint statement.