British Prime Minister Boris Johnson is in a stand-off with Taoiseach Leo Varadkar over the Brexit backstop amid a deterioration in Anglo-Irish relations.
Mr Johnson's failure to speak to Mr Varadkar nearly a week after he took office is being viewed in Government and diplomatic circles as evidence of Britain trying to "up the ante" over the backstop that it wants removed from the Brexit deal.
In a further sign of the widening chasm between the UK and the EU, Mr Johnson's spokeswoman signalled yesterday that he will refuse to meet EU leaders, including the Taoiseach, until they agree to ditch the backstop.
"I don't want the UK to be aloof or hanging back. I want us to engage, to hold out the hand, to go the extra mile, the extra thousand miles," Mr Johnson later said.
However, he reiterated that "the present withdrawal agreement is dead, the backstop must go".
Efforts were under way between officials in Dublin and London to organise a call between the two leaders last night, nearly a week after Mr Johnson took office.
The delay in the two leaders speaking is unprecedented in recent times.
"There has been contact at official level and it's expected that the Taoiseach and the PM will speak in the near future," Mr Varadkar's spokesman said.
A senior Government figure believes this is "part of a new British strategy to be seen to up the ante on the backstop".
A Government source acknowledged it was "out of the ordinary" that the pair had not spoken and a diplomatic source said this was not in keeping with practice.
Fianna Fail's Brexit spokesperson Lisa Chambers said: "I think it speaks to the deterioration in the relationship between Ireland and the UK that has been allowed to slip over the last three years in particular."
However another Government source cautioned it was "too early to draw conclusions", insisting much would depend on Mr Varadkar meeting Mr Johnson face to face.
However, Mr Johnson's spokeswoman said the prime minister would not hold face-to-face meetings with EU leaders unless they agree to renegotiate the backstop.
"The EU has said up to now it is not willing to renegotiate [the backstop]... the prime minister would be happy to sit down with leaders when that position changes," she said.
"But he is making it clear to everybody he speaks to that that needs to happen."
On a visit to Scotland, where he was booed by crowds ahead of a meeting with First Minister Nicola Sturgeon, Mr Johnson said he was "reaching out" to Mr Varadkar.
However, his stance on the backstop puts him on a collision course with Ireland and the EU.
In sharp contrast to the silence of recent days, Mr Varadkar spoke to Mr Johnson's predecessor Theresa May within two days of becoming Taoiseach in 2017.
Mrs May herself spoke to former Taoiseach Enda Kenny on the day she became prime minister, while Mr Kenny spoke to David Cameron by phone two days after the former Tory leader was re-elected in 2015.
Downing Street did not respond to queries.
A British Embassy spokesperson said: "Since taking office, the prime minister has spoken to a number of world leaders and he will continue to do so in the coming days."
Former taoiseach John Bruton said he does not believe the lack of a phone call makes any difference to the future relationship between the pair.
"What would they say if they had a call anyway? We all know from listening to the airwaves what Boris Johnson is saying," Mr Bruton said.