Taoiseach Leo Varadkar has said he "very much regrets" the statement by leader of the Democratic Unionist Party Arlene Foster who has effectively ended talks on the return of power-sharing in Northern Ireland.

"Power sharing and working together are the only way forward for Northern Ireland," the Taoiseach said.

"The Tánaiste and the Secretary of State are in close contact and we will continue to confer with the British government about the next steps," he added.

Separately, Tánaiste and Minister for Foreign Affairs Simon Coveney said Ms Foster's statement this afternoon was "very disappointing".

In her statement, the DUP leader said that after nearly four weeks of negotiations with Sinn Féin, the restoration of a devolved government was "not possible at this time."

Read Arlene Foster's statement in full

Mr Coveney said: "The Secretary of State (Karen Bradley) and I have spoken and will remain in close contact and I am briefing the Taoiseach on developments.

"As co-guarantors of the Good Friday Agreement, the UK and Irish governments have an obligation to uphold and protect the letter and spirit of that Agreement.

"We will need to reflect in the coming days on how best to do that."

SDLP leader Colum Eastwood expressed anger and disappointment at the development.

He said: "We have to get back to working together. We have to not allow this moment to be the destruction of all that we have achieved.

"Equally we can't allow this British government or this DUP to think that they are going to govern Northern Ireland on their own. That cannot be allowed to happen.

"The spirit which underpins the Good Friday Agreement is one that recognises we have two communities here, two nationalities, two sets of allegiances and we have to have that recognised in anything that goes after this.

Mr Eastwood warned that if the institutions fall, it would be "very, very difficult" to get them back up and running.

Alliance Party leader Naomi Long also described the latest development as "hugely frustrating".

Speaking in Stormont, she said: "We are in a very precarious position at this point in time, essentially in uncharted territory.

"We have now no prospect of a deal but also no process in place that could lead to a deal nor do we have any indication of willingness by parties to continue any such process."

She said political investment in devolution had been "swept away" over the most "minor of differences". 

UUP leader Robin Swann said Northern Ireland needs clarity.

Former DUP party member Nelson McCausland said there remained a deep gulf between the two parties, adding there is a feeling within the broad unionist community that there was a wrong approach to discussions.

Speaking on RTÉ's Drivetime, he said there needs to be a holistic conversation between both communities about the cultural differences that remain.

He said concessions should not be made for Sinn Féin in order to have devolved government back up and running again.

Mr McCausland said all linguistic traditions should be used as an example of cultural wealth and not cultural warfare.