The new Prime Minister said he was committed to “getting rid” of the Irish border backstop, which has long been a bone of contention in negotiations.
The EU’s chief Brexit negotiator, Michel Barnier, said removing the backstop guarantee was unacceptable.
Johnson also spoke on the phone with EU Commission President Jean-Claude Juncker.
Juncker reiterated the EU’s position that the already-negotiated withdrawal agreement was the best one possible – though he said the commission would be available over the coming weeks if the UK wanted to hold talks.
The withdrawal agreement negotiated by Theresa May “signed away” the UK’s economic independence and self-government as it allowed a free-flowing border between EU member Ireland and Britain’s Northern Ireland, known as a backstop.