Sir Elton said the boy had "stolen his heart"
Sir Elton John cannot adopt a 14-month-old boy because he is not married and too old, a Ukrainian minister has said.
The star, 62, said on Saturday that he hoped to adopt a boy, named Lev, whom he met while visiting an orphanage.
But government minister Yuriy Pavlenko told the Associated Press that the age difference between an adoptive parent and a child must be 45 years or less.
Sir Elton's civil partnership with David Furnish would not be recognised as a marriage in Ukraine, he added.
"Foreign citizens who are single have no right to adopt children... and the age difference between the adopter and the child cannot be more than 45 years," family, youth and sports minister Mr Pavlenko said.
"The law is the same for everybody - for a president, for a minister, for Elton John."
However, the BBC's Gabriel Gatehouse in Kiev says the question of whether Sir Elton's civil partnership can be recognised in Ukraine could still depend partly on politics.
Ukraine is entering election season and the issue of foreign adoptions is a sensitive one, he says.
If Sir Elton decides to proceed in the face of government opposition, the presidential candidates in next January's race could still sink his bid, he adds.
On Saturday, Sir Elton said at a press conference in Ukraine that the boy - whom he met at an orphanage for children whose lives had been affected by Aids and HIV - had "stolen my heart".
He and partner Furnish, 46, had always "talked about adoption", he said.
"David always wanted to adopt a child and I always said 'no' because I am 62 and I think because of the travelling I do and the life I have, maybe it wouldn't be fair for the child.
"But having seen Lev today, I would love to adopt him. I don't know how we do that but he has stolen my heart.
"And he has stolen David's heart and it would be wonderful if we can have a home. I've changed my mind today."
Sir Elton and filmmaker Furnish toured the orphanage as part of the singer's work with the Elton John Aids Foundation.