Tánaiste Simon Coveney says a Brexit deal is possible this week, but there is a lot of work left to do.

It is seen as a pivotal week, after European Union and UK negotiators failed to reach a deal over the weekend.

Talks aimed at replacing the backstop and securing a deal by Thursday's EU summit appear to have stalled.

There are just 18 days left until Britain is supposed to leave the EU and still a deal has not been reached.

Towards the end of last week, there was talk of a breakthrough after Taoiseach Leo Varadkar met the British Prime Minister Boris Johnson.

However over the weekend the talks have stagnated again.

The EU appears unconvinced about the viability of Northern Ireland leaving the customs union, but continuing to apply EU rules.

It would mean goods coming from the UK to the North would have to be checked and tracked to make sure the right tariffs are applied - something that remains difficult to enforce at a practical level.

Handout photo issued by the office of Leo Varadkar showing the Taioseach meeting British Prime Minister Boris Johnson in Cheshire, England ahead of private talks in a bid to break the Brexit deadlock | Image: Leo Varadkar/PA Wire/PA Images

Politically both sides are hopeful some agreement can be reached, but time is tighter than ever.

Typically any deal would have to be struck by Wednesday when the EU general affairs council meets, before the European Council leaders arrive in Brussels on Thursday to rubber stamp it.

While both sides will work until the last minute, this week's summit may be too soon.

In that case an extension of some kind may be sought - either a short technical one if a deal is in sight, or something longer to facilitate an election in the UK.

Tánaiste Simon Coveney speaks to reporters in Luxembourg | Image: © European Union

Speaking in Luxembourg ahead of an EU foreign affairs meeting on Syria, Mr Coveney says he is still hopeful of a last minute breakthrough.

"The message I would give is  that we need to be cautions - this is not an easy job.

"We've spent three years trying to get an agreement between the two sites and have made progress at different times - but certainly the last number of months have been difficult.

"A deal is possible and it's possible this month - it may even be possible this week.

"But we're not there yet - and as Michel Barnier said yesterday there's still a lot of work to do".

Meanwhile Sinn Féin leader Mary Lou McDonald is in London as talks continue.

At the weekend, the spoke with Mr Johnson by phone telling him there can be no return to the past.

Deputy McDonald said there can be no hardening of the border and no unionist veto.

She said: "Ireland did not consent to Brexit. The people of the north voted to remain.

"I reminded the British prime minister of this and of his obligations under Good Friday to ensure no hardening of the border.

"I told the the prime minister that any deal agreed must have legal and enduring guarantees that deliver for Ireland.

"There can be no customs border on our island. Our livelihoods, our economy and our peace must be protected.

"I also sought confirmation that there would be no veto gifted to DUP Brexiteers on protections for Ireland - such a position would be intolerable.

"The next week will be critical. Ultimately we need a deal that delivers for Ireland.

Prime Minister Johnson and I agreed to stay in contact and continue to engage on these and other important issues."

Reporting by Sean Defoe and Jack Quann