Boris Johnson is on "collision course" with the EU after warning he will not sign a Brexit deal unless the Irish backstop is "abolished".
In separate conversations with German Chancellor Angela Merkel and French President Emmanuel Macron, the new Prime Minister said Britain would never accept a repackaged version of Theresa May's deal, which was rejected three times by MPs.
The tough message followed a similar warning to European Commission chief Jean-Claude Juncker, who responded that the Withdrawal Agreement signed with May was "the best and only" deal possible.
The backstop stand-off sparked a warning from Irish Foreign Minister Simon Coveney that Johnson was putting Britain on course for a no deal exit.
Coveney said Johnson's stance was "very unhelpful".
"He seems to have made a deliberate decision to set Britain on a collision course with the EU and with Ireland in relation to Brexit negotiations.
"The approach the British Prime Minister seems to now be taking is not going to be the basis of an agreement, and that's worrying for everybody.'
Johnson issued a similar warning in a phone call with the German Chancellor.
Irish Prime Minister Leo Varadkar said Johnson appeared to be taking a "much harder line" than May, but had "demonstrated a degree of flexibility in the past" and wanted to discuss his "real red lines".
Hardline Eurosceptics, meanwhile, warned against a Brexit "betrayal", concerned Johnson could renege on his pledge to abandon May's deal.
On the Remain side, Wales Office Minister Lord Bourne resigned, saying: "I cannot accept a no deal Brexit."
In other developments Johnson cooled speculation of an early election by "absolutely" ruling out a snap poll, saying the public "don't want another electoral event, they don't want a referendum, they don't want a general election. They want us to deliver".