DUP leader Peter Robinson has asked a party colleague to step in as First Minister for a "short period", but insisted that he has acted ethically in the face of an "unfounded and mischievous allegation".
The move came just an hour after DUP colleagues backed Mr Robinson, who was under pressure to resign over the scandal surrounding his wife’s undisclosed financial dealings with her lover.
A BBC Spotlight programme reported last week that Iris Robinson secured £50,000 from two developers to fund a business venture for Kirk McCambley, with whom she was having an affair. The DUP is expected to formally announce this week that she is stepping down as an MP and member of the Northern Assembly with immediate effect.
Members of the Democratic Unionist Party had just earlier today given Mr Robinson their full backing.
“This has been a difficult time however; I want to thank all those who have sent messages of encouragement and support. I have literally received thousands of messages from all sections of the community and beyond," Mr Robinson said in a statement.
He said his wife was receiving acute psychiatric treatment through the Belfast Health and Social Care Trust.
"As a father and a husband, I need to devote time to deal with family matters.
"To take account of this I have, following a meeting with party colleagues and one with the Deputy First Minister, asked the Minister for Enterprise, Arlene Foster MLA to carry out the functions of the office of First Minister for a short period."
Mr Robinson said he appreciated the unanimous support from the DUP his morning. "I want to publicly thank them for all their support and kindness to me."
He said it was "a great honour and privilege to lead the Democratic Unionist Party" and that he would continue to do so with "the full support" of his colleagues.
"I continue to contend I have acted ethically and it is particularly painful at this time of great personal trauma that I have to defend myself from an unfounded and mischievous allegation. As you know I have requested that an opinion be obtained from senior counsel in relation to the Ministerial Code and related aspects. In addition the deputy First Minister has received advices from the Departmental Solicitors’ Office which do not present any complications of difficulties whatsoever."
Mr Robinson said he had asked that a Parliamentary and Assembly inquiry into these matters be undertaken.
"Throughout this period I will continue to work on the outstanding issues relating to policing and justice and some other matters. This allows a particularly concentrated focus on these discussions and we will work to try to build on the agreements we have already reached so that a successful resolution can be reached.
"This is the year to deliver at Stormont for all the people of Northern Ireland.”
Mr Robinson said he wanted to respond to everyone who had taken the time to send their best wishes to him and his family. "I hope they will forgive me because of the volume if it takes me some time."
Taoiseach Brian Cowen said he welcomed Mr Robinson's decision "to continue to work on the crucial issue of
devolution of policing and justice and his commitment to a successful resolution".
He also offered his best wishes to Arlene Foster in her new role.
Assembly speaker William Hay earlier told surprised politicians in the Assembly chamber that Ms Foster had been asked to take on the functions of First Minister with immediate effect. He said he was calling a meeting of party whips to discuss the surprise move.
Stormont officials said the procedural device could last for six weeks - sparking claims that Mr Robinson may be providing himself with a window of opportunity to clear his name.
Ms Foster said ahead of the other official investigations into Mr Robinson's conduct that departmental solicitors in the Office of the First and Deputy First Minister had already indicated that Mr Robinson did not break any rules.
“The departmental solicitors’ office has already considered the allegations made in the Spotlight programme and has advised Peter Robinson that he was not in breach of the ministerial code, the pledge of office, the ministerial code of conduct of the seven principles of public life, so I think it’s important to say that.”
She said she was also sure the senior lawyers commissioned to investigate Mr Robinson’s actions would find no evidence of wrongdoing.
“I am personally confident, my party is very confident, that this will confirm that Peter Robinson, the First Minister, acted entirely properly at all times, but let’s have this [investigation] and let’s have it quickly.”
Some 30 party officers and Assembly members met at Stormont this morning to consider their leader's future.
"It was unanimously agreed that despite attempts by elements in the press and our political opponents to force ... Peter Robinson to resign as party leader, we offered him our wholehearted support and our desire that he remain in office as the Democratic Unionist Party leader," the party's deputy leader Nigel Dodds told reporters after the meeting.
DUP Lagan Valley MP Jeffrey Donaldson said Mr Robinson was entitled to due process and should not be tried by the media.
Former first minister and UUP leader David Trimble said yesterday he expected Mr Robinson’s resignation within days.
Meanwhile, the British and Irish governments are maintaining high-level contacts to ensure the personal and political crisis affecting the Robinson family and the DUP does not collapse the Stormont powersharing administration.
Taoiseach Brian Cowen and British prime minister Gordon Brown are concerned the drama affecting the Robinsons could topple the Northern Executive and Assembly.
With the Stormont institutions already under pressure from the DUP/Sinn Féin stand-off on policing and justice, Northern Secretary Shaun Woodward is due to hold talks in Dublin tomorrow with Minister for Foreign Affairs Micheál Martin. Mr Woodward made it clear that Mr Robinson “must be allowed the time and space” to address his personal family issues.
Sinn Féin spokesman on policing and justice Alex Maskey said today the transfer of policing and justice powers to the North was "long overdue" and had to be addressed urgently by the British and Irish governments.
Mr Maskey said although there was "massive sympathy" for the Robinson family, Sinn Féin had to deal with the political fallout from the controversy. "Whoever the DUP may have as leader . . . the question [the transfer of powers] has to be addressed by that party and by both governments," Mr Maskey told RTÉ radio.
Additional reporting: PA