The Taoiseach has said that more progress from the British government is needed on the border in the next two weeks ahead of a European Council meeting.
Speaking in the Dail, Leo Varadkar said that if this does not happen, the council will not be in a position to state that real and meaningful progress has been made.
He said that could bring into question whether it is possible to agree a withdrawal agreement by the October deadline.
Mr Varadkar said it often seemed like the UK was negotiating with itself.
However he said the EU was united and from a position of strength 'we would get the outcome we want'.
He described the British proposals on custom arrangements as a partial solution as it deals with customs not with regulation.
Earlier, Tánaiste and Minister for Foreign Affairs Simon Coveney updated the Cabinet on the progress of the Brexit negotiations, ahead of the European Council meeting.
It was the first opportunity for ministers to discuss the British government's proposals on the customs union that were published last week.
British Prime Minister Theresa May's recent proposals for a 2021 deadline for a final agreement and an end to all of the UK conforming to EU custom regulations were firmly viewed by Ireland as a first step with more work needed.
The Cabinet was also briefed on the contingency plans by Government departments and agencies.
Logistical planning for pension and social welfare payments to non-EU citizens within the common travel area post-Brexit will also be discussed.
With the Government's focus now clearly on the European Council meeting, the Tánaiste travelled to Germany today and Taoiseach Leo Varadkar to Spain later this week.
However, they are keeping a close eye on Westminster and the outcome of votes on the EU Withdrawal Bill today and tomorrow.
Fianna Fáil spokesperson on Brexit, Lisa Chambers, has said it is crunch time for the negotiations.
Deputy Chambers said the Government oversold the backstop deal reached last December.
Labour leader Brendan Howlin said the prospect of a hard Brexit and a hard border is now a real threat.
Meanwhile, more high level training in customs clearance must be provided here to deal with the fallout from Brexit.
This was one of the main findings of a recent study by the Government's Expert Group on Future Skills Needs.
The report was one of two pieces of research brought to Cabinet by the Minister for Business, Enterprise and Innovation Health Humphreys.
The second report looked at the implications of Brexit on the 15 sectors that are considered to be most exposed economically.
These include the agri-food, chemical and pharmaceutical sectors.
The survey carried out jointly by the Department of Business and Deloitte found the greatest level of concern related to the free movement of goods and possible tariffs.
The study, which ran from February to August last year, revealed that only half the 15 sectors examined were taking action to deal with the potential impact of Brexit.
Additional reporting Mícheál Lehane