Boris Johnson has set out his demands for renegotiating Britain's exit from the European Union - in a move one EU diplomat dismissed as "pure PR".
In a letter to European Council President Donald Tusk, Johnson insisted that an insurance policy for the Irish border be removed from the Brexit deal - calling it "anti-democratic".
The EU has consistently refused to reopen the Withdrawal Agreement agreed by Johnson's predecessor Theresa May last year.
But the riddle over what to do with the EU's only land border with the UK has repeatedly imperiled talks.
The EU wants to ensure the border does not become a back door for goods to enter the EU's single market, but Ireland says a hard border could undermine the 1998 Good Friday Agreement which brought peace after three decades of conflict.
And the UK does not want any virtual border whereby Northern Ireland would be kept more closely aligned with the EU - saying this is inconsistent with the UK's sovereignty.
The Irish backstop was a compromise - keeping the United Kingdom in a customs union until a better solution was found.
But Brexiteers fear it would leave the UK dependent on rules set in Brussels, and hinder efforts to strike trade deals with other countries.
Johnson - who meets with France's Emmanuel Macron and Germany's Angela Merkel this week - wrote that the backstop should be replaced with a "commitment" to put in place alternative arrangements.
He also claimed that it is the backstop that could weaken the delicate balance between nationalists and unionists in Northern Ireland.
That was dismissed by Dublin, with an Irish government source adding that Johnson had given no details over what any alternatives would be.
Tusk responded on Twitter, saying that anyone who is against the backstop without proposing any realistic alternatives is supporting the reestablishment of a hard border - "even if they do not admit it".