Mrs Long was speaking after Sinn Fein said the discussions had run their course and it would not be nominating a deputy First Minister tomorrow.
“The issues themselves have been on the table for many years and through many negotiations, so it is extremely disappointing and frustrating agreement has not been reached,” she said.
“The differences are not insurmountable and agreement within the three week timescale was achievable. However, whilst we remain available and willing to engage to ensure the 4pm Monday deadline is met and devolution restored, the prospect of that now looks remote.
“While the obstacles to agreement are relatively minor, the consequences could not be more serious. For the first time in the 96-year history of Northern Ireland, we will be without any legal, political authority.
“We are days away from the end of the financial year, yet there is no Budget. We are days from the triggering of Article 50, yet we have no Brexit plan. We are already overdue the Assembly vote needed to set next year’s regional rate yet we have no Assembly. We have no Programme for Government and no Government to agree one.
“Already in the voluntary and community sector and in our key public services like health and education, the effects of this political vacuum are being felt with restricted budgets, increased uncertainty and job losses. Parties owe it to those who rely on and who deliver vital services to continue to press for an urgent settlement.
“Despite our anger at this failure, we remain committed to do all we can to resolve this impasse. There is no alternative to devolution that will resolve these issues or serve our constituents well – neither an election nor direct rule will solve anything.
“Parties need to step up and get real, and give the British Government a good reason to give an extension to the talks process. That over 20 years of progress would be squandered so lightly is simply unthinkable.”