Boris Johnson has backed the hospital treating terminally ill Charlie Gard and stressed that any decisions made about his care should be in his "best interests".
The Foreign Secretary told his Italian counterpart it is "right that decisions continued to be led by expert medical opinion, supported by the courts", after the Vatican's paediatric hospital offered to care for the young boy.
Charlie's mother has spoken to doctors at the Bambino Gesu hospital in Rome and medics are in touch with international and US experts about the 11-month-old's treatment, a spokesman for the hospital said.
Charlie has been at the centre of a lengthy legal battle involving his parents, who want to take him to the US for experimental therapy, and doctors at Great Ormond Street Hospital (GOSH).
Bambino Gesu hospital asked GOSH if Charlie could be transferred there after Pope Francis called for Charlie's parents to be allowed to "accompany and treat their child until the end".
Mr Johnson discussed the case with Italian Foreign Minister Angelino Alfano as part of a scheduled telephone call.
A spokeswoman for the Foreign Office said: "Minister Alfano also raised the case of Charlie Gard and the Pope's recent offer of treatment in Italy.
"The Foreign Secretary said this was a deeply tragic and complex case for all involved, and said it was right that decisions continued to be led by expert medical opinion, supported by the courts, in line with Charlie's best interests."
Bambino Gesu hospital said it was in discussions with the English authorities and Charlie's family about a possible transfer.
But it has been told a move would not be possible unless it agreed to follow the Supreme Court's ruling, a hospital spokesman said.
Charlie is suffering from a rare genetic condition and has brain damage and no one can be certain whether or not he feels pain, GOSH has said.
Successive legal attempts by Charlie's parents failed as judges in the High Court, Court of Appeal and Supreme Court in London ruled in favour of GOSH doctors, while the European Court of Human Rights declined to hear the couple's appeal.
Charlie's parents, Chris Gard and Connie Yates, are now spending the last days of his life with him.
Theresa May has said she is "confident" that GOSH would consider any offers or new information relating to the child.
The Prime Minister told MPs: "It is an unimaginable position for anybody to be in and I fully understand and appreciate that any parent in these circumstances will want to do everything possible and explore every option for their seriously ill child.
"But I also know that no doctor ever wants to be placed in the terrible position where they have to make such heartbreaking decisions."
Charlie's plight has attracted international attention, with both US President Donald Trump and the Pope tweeting their support.
More than £1.3 million has been raised in donations to help the family take Charlie to the US for therapy.
Mrs May said: "I am confident that Great Ormond Street Hospital have and always will consider any offers or new information that has come forward with consideration of the wellbeing of a desperately ill child."
At Prime Minister's Questions, the family's MP Seema Malhotra said it was "clear that if Charlie remains in the UK there is no further treatment available and that life support will be switched off".
The Feltham and Heston Labour MP urged Mrs May to do "all she can" if there was the possibility of Charlie being flown to the US for treatment.
But renowned scientist and genetics expert Professor Robert Winston has criticised attempts to transfer Charlie from the central London specialist children's hospital.
"I think, first of all, one has to accept the loss of a child is about the worst injury that any person can have and, secondly, I think the autonomy of parents is probably sacrosanct because a child can't give approval, can't give consent," he told ITV's Good Morning Britain.
"But having said that, these interferences from the Vatican and from Donald Trump seem to me to be extremely unhelpful and very cruel, actually, because this child has been dealt with at a hospital which has huge expertise in mitochondrial disease and is being offered a break in a hospital that has never published anything on this disease, as far as I'm aware."
The High Court considered evidence from a specialist who would oversee any treatment Charlie had at a hospital in the US.
The specialist, who cannot be named for legal reasons, said therapy would provide a "small chance" of a meaningful improvement in Charlie's brain function.
A spokesman for Bambino Gesu said it was working to solve the "legal problem", while GOSH declined to comment.
Charlie's parents, both aged in their 30s and from Bedfont, west London, have been given more time with their son before his life support is turned off.