Charlie Gard's parents say they have been denied their final wish to be able to take their son home to die.
Chris Gard and Connie Yates, both in their 30s from Bedfont, west London, wanted 10-month-old Charlie, who suffers from a rare genetic condition and has brain damage, to be allowed to die at home.
But they say Great Ormond Street Hospital (GOSH) has denied them this request and the baby's life-support will be switched off on Friday.
Alongside a video posted on YouTube, Charlie's parents said: "We are utterly heartbroken spending our last precious hours with our baby boy.
"We're not allowed to choose if our son lives and we're not allowed to choose when or where Charlie dies.
"We, and most importantly Charlie, have been massively let down throughout this whole process.
"Charlie will die tomorrow knowing that he was loved by thousands... thank you to everyone for all your support!"
The couple also claim they are being rushed, despite having been promised they would have all the time they needed to say goodbye to their son.
In a video on MailOnline, Mr Gard said: "Our final wish if it all went against us, and we have had this conversation many times, if we lose can we take our little boy home, to where he belongs, to die? And we are not allowed.
"We know what day our son is going to die and we don't even get a say in what happens to him.
"He's got to die in that place."
Charlie's parents said the hospital also said no to the baby dying in a hospice, and refused their offer to arrange private transport to their home.
A spokeswoman for Great Ormond Street Hospital said: "As with all of our patients, we are not able to and nor will we discuss these specific details of care.
"This is a very distressing situation for Charlie's parents and all the staff involved and our focus remains with them."
Ms Yates described the day Charlie was born, August 4 last year, as the best day of their lives but said June 30 2017, would be the worst.
Charlie's parents wanted their son to undergo a therapy trial in the US, but specialists at GOSH said it was experimental and would not help.
They had asked European court judges in Strasbourg, France, to consider their claim after judges in the High Court, Court of Appeal and Supreme Court in London ruled in favour of Great Ormond Street doctors.
But on Tuesday the European Court of Human Rights refused to intervene.