Gerry Adams has said the Northern Ireland political process faces its greatest challenge since the Good Friday Agreement negotiations.
He criticised Democratic Unionist Party leader Peter Robinson for not showing enough progressive leadership and claimed anti-agreement unionists had been allowed to set the agenda, undermining the devolved power-sharing government at Stormont.
Sinn Féin and the DUP, the two largest parties in the mandatory coalition, have been at loggerheads over welfare reform and plans for a peace centre at the site of a former high security prison near Belfast.
Mr Adams told the BBC: "The crisis is clearly a political crisis but the fact is citizens need to have confidence in the political institutions and because one of the biggest parties, the biggest party in the Executive (DUP), is not committed to what it signed up to when it went into government with Sinn Féin and the other parties, that confidence is being eroded.''
The Sinn Féin president accused unionists of failing to engage positively in political negotiations surrounding contentious flags, parades and dealing with the toxic legacy of thousands of deaths during the conflict.
Dialogue has been stalled in a unionist protest over the handling of a loyal order parade in North Belfast.
The Irish Government has said it hopes talks can resume next month.
But Mr Adams said the stance of unionists meant there was no likelihood of negotiations resuming.