Relations on the Executive have totally broken down - Villiers
The British Government has said working relations on the Northern Ireland Executive have completely broken down.
Northern Ireland Secretary Theresa Villiers said she would not suspend the devolved institutions following the resignation of DUP ministers including Peter Robinson.
However, she said that the situation was very grave.
"It is a sign of a complete breakdown in the working relationships within the Executive.
"Powersharing only works effectively if you can have effective relationships between parties from different sides of the community and different parts of the political spectrum," said Ms Villiers.
She and the Republic's Foreign Affairs Minister Charlie Flanagan are chairing talks at Stormont between the five largest Northern Ireland parties.
"I will be working and continuing to work with determination with the Prime Minister, with the Northern Ireland parties and with colleagues in the Northern Ireland Government to get a way through these crises and find a resolution to the hugely important challenges we now face," she said.
"We did not think the circumstances will justify suspension, that has not changed and suspension would not resolve the two big problems - implementation of the Stormont House Agreement and the presence of paramilitary organisations.
"The only way those problems are going to be resolved is through intensive cross-party talks. I think time is very short because of the seriousness of the situation, I think that today's events make the situation much more serious.
"Paramilitaries were never justified, they need to disband. There is more that can be done to work towards the day when those organisations are a bit of Northern Ireland's past, not its present."
Mr Flanagan urged the North's political leaders to "take a step back and consider the gains achieved over recent years, the benefits to the people of Northern Ireland and what is now at stake".
"I encourage all parties to reflect carefully," he added.
"The Secretary of State and I will be here in Stormont House on Monday morning and I invite the parties to join us for discussions on how we find a way through the current serious impasse. We will, of course, remain available to the parties over the weekend."
Mr Flanagan said his department, with the strong support of Taoiseach Enda Kenny and Tánaiste Joan Burton, have been working with the Secretary of State and the Northern Ireland parties to resolve the critical issues which threaten the power-sharing institutions.
"What we want is for the devolved powersharing Executive and Assembly to work as envisaged in the Good Friday Agreement and deliver peace, prosperity and reconciliation for the people of Northern Ireland," he added.
A Downing Street spokesman said David Cameron spoke with Peter Robinson and told him the UK Government did not believe it would be right to introduce emergency legislation now to suspend the Assembly.
"The PM underlined the need for intensive cross-party talks to identify ways to tackle all paramilitary groups and to get on with implementation of the Stormont House Agreement," the spokesman added.