Northern Ireland's Deputy First Minister Martin McGuinness announced his resignation Monday, calling for an election to resolve a scandal sparked by a troubled energy initiative.
"Therefore it is with deep regret and reluctance that I am tendering my resignation as deputy First Minister", McGuinness said in a statement.
He cited the Democratic Unionist Party's (DUP) conduct over the scandal surrounding the Renewable Heat Incentive (RHI) scheme as the reason.
McGuinness's resignation could trigger new elections to the region's power-sharing assembly, pitching Northern Ireland into chaos as talks on the terms of the U.K.'s exit from the European Union approach.
The scheme aimed to encourage businesses to burn wood pellets rather than fossil fuels.
Martin McGuinness is to resign as deputy First Minister of Northern Ireland. She said it was "clear that Sinn Fein's actions are not principled, they are political".
"She can express as much confidence as she can muster about how an investigation in the limited form she wants would exonerate her for the budgetary debacle that RHI became, but she needs to show contrition, not just in relation to the underlying flaws in that scheme but also for her mishandling of the political accountability crisis which now exists".
Sinn Fein leader Gerry Adams had said at the weekend that there was a conflict of interest if Foster remained in power. "That position is not credible or tenable".
Northern Ireland Secretary James Brokenshire said that unless Sinn Fein nominates a replacement in the next seven days, he would have no choice but to call an Assembly election. In recent years he has voiced his concerns over a number of issues where the DUP has been embroiled in a number of financial scandals and failure to approve funding requests for inquests into murders that happened during Northern Ireland's Troubles.
And at yesterday's Stormont press conference, the only reference to Mr McGuinness came from Ms O'Neill, who insisted he was central to decision-making around the RHI saga.
However, Mr McGuinness was nowhere to be seen.
Sinn Fein, which campaigned for the United Kingdom to stay in the European Union, says Foster has failed to properly represent the 56 percent of Northern Ireland voters who voted "Remain".