Rishi Sunak has said he is "concerned" about the impact of Scotland's landmark gender reforms on the rest of the UK.
The Scottish Government passed the Gender Recognition Reform Bill last month - making it easier for transgender people to legally change gender.
The legislation removes the requirement for a medical diagnosis of gender dysphoria in order to obtain a gender recognition certificate.
But just hours after it passed, Scotland Secretary Alister Jack raised the possibility of it being blocked.
Mr Sunak expressed concern about the impact of the bill on his first official visit to Scotland, after holding talks with Nicola Sturgeon amid strained relations between London and Edinburgh.
The Prime Minister told Good Morning Scotland: "Obviously, this is a very sensitive area and I know there were very robust and debates and exchanges on it as the bill was passing in Scotland.
"But what I'm concerned about is the impact of the bill across the United Kingdom. As is entirely standard, the UK Government would take advice on that."
No10 insisted no "final decision" had been made on whether ministers will use a Section 35 order - which allows Westminster to intervene - to scupper the new law.
Tory minister must decide next week whether to act - and could face a legal challenge from the Scottish Government if they block the legislation.
A spokesman for the Prime Minister said: "We've spoken before about our belief that we need to balance strike the right balance and we think that the balance is correct and the Gender Recognition Act which provides the proper checks to allow people to legally change their sex if they want to.
"They want to you'll know that every bill that passes through Parliament is paused for four weeks before proceeding to royal assent but as we are today we haven't made a final decision on a potential action at this time."
But SNP Westminster leader Stephen Flynn said the UK Government should not block the bill.
He told the programme: "This is not just a question about the GRR (Gender Recognition Reform Bill) or people's individual views on it. This is about democracy.
"The Scottish Parliament has voted in favour of legislation that sits within devolved competencies, and it's incumbent upon Westminster to ensure that legislation is passed in full."
In December, Mr Sunak said it was "completely reasonable" for the Government to consider the controversial move to block the legislation.
Similar proposals were laid out by ex-PM Theresa May in 2017 but were shelved by Liz Truss, who was equalities minister during Boris Johnson's Government.
Mr Sunak flew to Inverness on a private jet for his two-day visit to Scotland, Downing Street admitted.
He is understood to have used an RAF plane for the trip, only days after he was criticised for taking a 36-minute flight to Leeds to visit a health centre.
A No 10 spokesman said: "We always take decisions on the Prime Minister's transportation with consideration as to the best use of his time and the best use of taxpayer funding.
"In this instance, travelling up by plane allowed him to have that meeting last night with the First Minister."
