Irish prime minister Leo Varadkar on Wednesday said that the UK and European Union would have to agree on a “no-deal deal” to prevent a hard border in Northern Ireland if the UK crashes out of the bloc in March 2019.

“If we did end up in a no-deal situation, we would find ourselves having to negotiate a no-deal deal quite soon thereafter,” he said, speaking in Ireland’s parliament.

In the event of a no-deal Brexit, the UK’s trading relationship with other countries will be governed by World Trade Organisation (WTO) rules.

An agreement relating to “regulations and customs” would be necessary, Varadkar said, “to avoid a hard border,” and allow the UK to honour its WTO obligations, and Ireland its own obligations as an EU member.

He noted, however, that “nobody knows for sure” what would happen in the event of a no-deal Brexit.

Though there is no specific rule that requires a country to secure its border, the UK may be forced to erect a border if other members see its absence as a breach of the organisation’s “most-favoured-nation” principle, which prevents a country from discriminating between its trading partners.

Concerns about a no-deal scenario have jumped in recent days, following a spate of ministerial resignations in the UK and increasing unrest within the Conservative Party’s Eurosceptic wing about the Brexit deal that prime minister Theresa May negotiated.

But Varadkar said it was not “inevitable” that May would fail to get the deal through parliament.