Ireland's Prime Minister (Taoiseach) and Defence Minister Leo Varadkar holds a news conference at the European Union leaders summit in Brussels, Belgium October 18, 2018. REUTERS/Francois Lenoir

BRUSSELS (Reuters) - Irish Prime Minister Leo Varadkar said on Friday that a possible extension of Britain’s post-Brexit transition period would not diminish Ireland’s need for a “backstop” to avoid a hard border with Northern Ireland.

He also told reporters on the third day of EU summit meetings in Brussels that it would be up to British Prime Minister Theresa May to decide whether she had to defy opposition from her unionist Northern Irish allies and agree to the EU’s proposed backstop, which would potentially create trade barriers between Northern Ireland and the British mainland.

He said it was a “judgment call” May would have to make but said that without an Irish backstop, any withdrawal treaty might not be ratified by the European Parliament. He acknowledged that May faces a difficult domestic political situation, running a minority government with internal divisions on the Brexit issue.

Varadkar also renewed a warning that a return of customs posts on his country’s border with Northern Ireland could see a return to violence in the British province:

“Certainly it’s something that’s in the back of my mind as a potential consequence if we get this wrong.”

On the issue of extending Britain’s transition period, he said: “I’m open to the idea of an extension or a longer transition period, but that’s not an alternative to a legally binding Irish backstop. So, certainly not an alternative, it’s just something that might be part of the mix.”