The Irish Prime Minister says Brexit is framing relations between Ireland and Britain.
Taoiseach Leo Varadkar says he also "undermined" the Good Friday Agreement (GFA).
The GFA was signed by political parties in Northern Ireland in 1998 and was supposed to make peace after 30 years of The Troubles
The Irish border is one of the biggest points in the Brexit negotiations.
"Anything that spreads the communities in Northern Ireland undermines the Good Friday Agreement, and anything that pulls Britain and Ireland apart undermines that relationship," Varadkar said of RTE program Marian Finucane.
Mr. Varadkar also said he has a good relationship with DUP boss Arlene Foster.
He said that the DUP and Sinn Féin would have to come together and reach agreement to get the Stormont Assembly back up and running.
Northern Ireland has been without an executive since January 2017, when the rulers – the DUP and Sinn Féin – split into a bitter series.
Mr Varadkar said that if Brexit were to be reasonably clear over the next few weeks or months, there would be an opportunity to get the executive running again.
He also said that Ireland is facing a potentially difficult time, even if an agreement is reached.
How do you solve a problem like the Irish border?
The United Kingdom and the EU both want to avoid a "hard border" between Northern Ireland and the Republic of Ireland, which may include physical controls or infrastructure, but can not agree.
An essential part of the negotiations is the controversial border crossing.
The backstop is the last resort to protect an open barrier on the Irish island should the United Kingdom leave the EU without a comprehensive deal.
What do "controls in the Irish Sea" mean?
In an emergency situation, there could theoretically be two types of checks on the Irish Sea:
- inch – ensure that the correct EU tariffs have been paid
- Regulatory – Ensure that goods comply with EU safety and quality standards
The government has insisted that it would never accept Irish Sea Customs inspections.
However, care was also taken not to completely rule out the prospects of supervisory controls.