Update: The EU's chief Brexit negotiator says any time limits on the backstop aimed at avoiding a hard border would be useless.
Michel Barnier has told a French newspaper that only having the measure in place for a certain period would be like taking out home insurance for five years and having a problem after six.
He also said there will have to be checks on the Irish border if Britain leaves without a deal.
Mr Barnier told Le Monde, Rzeczpospolita and Luxemburger Wort that the current backstop proposal over the border was the only option available.
Mr Barnier said: "The question of limiting the backstop in time has already been discussed twice by European leaders. This is the only possible option because an insurance is of no use if it is time-limited."
Sinn Féin leader Mary Lou McDonald has said that European Commission spokesman Margaritis Schinas is right when he says there would need to be a hard border in Ireland in the event of a no-deal Brexit.
That is why the backstop is so important, she told RTE’s Morning Ireland, as it mitigates the effect of Brexit in the event of the UK “crashing out” with no agreement.
The Government needs to “hold its head” and has the responsibility to start preparing for that eventuality, she said.
The first job is to look for “breathing room” for Irish businesses, for society in general and for peace structures.
Ms McDonald dismissed reports that the Taoiseach Leo Varadkar had told other party leaders that the absence of a single market border in Ireland could mean checks at ports in France or the Netherlands is a "desirable" option if there is a no-deal Brexit.
Reports had suggested that it was one of the options mentioned in a discussion around what might happen if there is no withdrawal agreement.
However, Ms McDonald said such a suggestion “was not a runner” and that the Taoiseach had not proposed it at their meeting.
She said: "He didn't set that up as a proposition or a desirable outcome.
"I have emphasised to the Taoiseach that the task now for him and his government is to hold their nerve."
A Border Poll was “not something in Never Never Land,” she said. The Good Friday Agreement was “the ultimate backstop”.
“The border is not just an Irish problem – it’s a European problem.”