Failure for the UK and European Union to reach an agreement on a post-Brexit trade deal would be "very, very damaging all around", Taoiseach Micheal Martin said.
Talks between the two parties have been taking place in London this week, but they are not expected to bear fruit despite progress needing to be made soon if a new deal is to be in place when the current arrangements expire.
The EU wants a deal by mid-November in order for it to be ratified by the time the transition arrangements expire at the end of the year and the UK leaves the customs union and single market.
Without a deal being struck, trade between the UK and EU will be subject to tariffs set out by the World Trade Organisation.
Speaking to the BBC, the Irish premier said failing to secure a deal would be "ruinous" for the UK, and that Ireland would also suffer.
He told the broadcaster: "We've all had a very significant shock to our economic system because of Covid-19 – the last thing we need now across all of our respective economies is a second major shock."
Mr Martin also said the UK needed to be "very careful that they do not do anything that could destabilise the politics of Northern Ireland", and that no deal past the transition period could lead to "tensions that are unnecessary".
Steve Bray the anti-Brexit protester
Steve Bray the anti-Brexit protester
Steve Bray has finally admitted defeat in his campaign against Brexit (SWNS)
Mr Bray took to the streets for a final time after the Tories won a majority in the general election (SWNS)
The campaigner wore a grey hat and flag cape on his 847th day of protest (SWNS)
LONDON, ENGLAND - JANUARY 08: Anti-Brexit protester Steve Bray (L) and a pro-Brexit protester argue as they demonstrate outside the Houses of Parliament in Westminster on January 08, 2019 in London, England. MPs in Parliament are to vote on Theresa May's Brexit deal next week after last month's vote was called off in the face of a major defeat. (Photo by Jack Taylor/Getty Images)
Anti Brexit protester Steve Bray shouts a comment against Boris Johnson in Westminster as inside Parliament the Tory leadership race continues on 17th June 2019 in London, England, United Kingdom. (photo by Mike Kemp/In Pictures via Getty Images)
(left to right) Andy Wigmore and Leave.EU founder Arron Banks are confronted by anti-Brexit campaigner Steve Bray as they leave the Houses of Parliament in Westminster, London. Picture dated: Wednesday March 27, 2019. Photo credit should read: Isabel Infantes / EMPICS Entertainment.
Vince Cable, leader of the Liberal Democrats and his wife Rachel Smith pose with Anti-Brexit protester Steve Bray after a news conference following the results of the European Parliament elections, in London, Britain May 27, 2019. REUTERS/Hannah Mckay
Vince Cable, leader of the Liberal Democrats and new Members of the European Parliament Irina von Wiese, Dinesh Dhamija and Luisa Porrit pose with Anti-Brexit protester Steve Bray during a news conference following the results of the European Parliament elections, in London, Britain May 27, 2019. REUTERS/Hannah Mckay
Anti-Brexit protester Steve Bray demonstrates outside the gates of Downing Street, as uncertainty over Brexit continues, in London, Britain May 7, 2019. REUTERS/Henry Nicholls
Anti-Brexit protester Steve Bray demonstrates outside Labour Party's headquarters, as they hold their National Executive Committee meeting, in London, Britain April 30, 2019. REUTERS/Toby Melville
Mark Francois (left), Conservative MP for Rayleigh and Wickford, and the vice-chairman of the European Research Group (ERG), in conversation with anti-Brexit campaigner Steve Bray at College Green in Westminster, London.
REFILE - REMOVING EXTRA WORDS Anti-Brexit protester Steve Bray is seen outside the Houses of Parliament in London, Britain, April 8, 2019. REUTERS/Gonzalo Fuentes
Britain's Conservative Party MP Jacob Rees-Mogg walks as anti-Brexit protester Steve Bray demonstrates outside the Houses of Parliament in London, Britain, April 3, 2019. REUTERS/Peter Nicholls
(right) Dominic Grieve MP is confronted by anti-Brexit campaigner Steve Bray on his way to the Houses of Parliament in Westminster, London. Picture dated: Wednesday March 27, 2019. Photo credit should read: Isabel Infantes / EMPICS Entertainment.
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The Fianna Fail leader told the Dail this week any deal would need to "lead to a neutralisation of the offending clauses of the Internal Markets Bill" and lead to "strict adherence to the protocol and the Withdrawal Agreement".
He added that he welcomed the decision taken in the House of Lords on Monday in relation to the Bill, which contains controversial measures seeking to tear up parts of the Brexit divorce agreement.
And he told the BBC: "Efforts have to be made to reassure the EU side that what has happened in terms of the Internal Market Bill is not going to happen in 12 months' time in the event of a deal being agreed between the European Union and the United Kingdom."
The main stumbling blocks between the UK and EU are thought to include the "level playing field" measures aimed at preventing unfair competition on issues including state subsidies, the ongoing row over fishing rights and how any UK-EU deal will be governed.
Stefaan de Rynck, an adviser to Mr Barnier, insisted the EU side had been willing to compromise in the negotiations – implying that it was British resistance which had prevented progress.
"The EU has been in compromise mode at all negotiation tables, for months," he tweeted on Wednesday.