The mother of a 12-year-old boy left in a comatose state after suffering brain damage has written an urgent appeal to the government, with support treatment understood to be ending on Monday afternoon.

In a letter sent on Saturday, Hollie Dance urged the health secretary to “act immediately” to stop her son Archie Battersbee’s treatment ending.

Barts health NHS trust, which is caring for Archie, is understood to be going ahead with plans to end the support at 2pm on Monday.

Writing to Stephen Barclay, Dance said: “If this happens, this will be an extraordinary cruelty, and a flagrant breach of Archie’s rights as a disabled person.

“Archie is entitled to have the decisions about his life and death, taken by the NHS and UK courts, to be scrutinised by an international human rights body. Hastening his death to prevent that would be completely unacceptable.

“I trust that you will now act immediately, as a member of the government responsible for the NHS, to ensure that this does not happen, and our country honours its obligations under the international human rights treaties which we have signed and ratified.”

A high court judge has ruled that ending treatment is in Archie’s best interests, after reviewing evidence.

Dance and Paul Battersbee, Archie’s parents, who are separated and both live in Southend, Essex, failed to persuade court of appeal judges to overturn that ruling and supreme court justices have refused to intervene.

Archie’s parents are being supported by campaign organisation the Christian Legal Centre.

They have asked the United Nations to intervene in a “last-ditch” application.

The UN committee on the rights of persons with disabilities has written to Archie’s parents and their legal team saying it had “requested the state party [the UK] to refrain from withdrawing life-preserving medical treatment, including mechanical ventilation and artificial nutrition and hydration, from the alleged victim while the case is under consideration by the committee”.

It added: “This request does not imply that any decision has been reached on the substance of the matter under consideration.”

The family said stopping treatment would be in breach of the UK’s obligations under international human rights law.

Archie’s parents have asked hospital bosses to continue treatment until the UN has considered the case.

Judges in London have heard that Dance found Archie unconscious with a ligature over his head on 7 April.

She thinks he might have been taking part in an online challenge.

He has not regained consciousness.

Doctors treating Archie at the Royal London hospital in Whitechapel, east London, think he is brain-stem dead and say continued life-support treatment is not in his best interests.

Alistair Chesser, chief medical officer for Barts health NHS trust, said on Friday that “further delay” in starting to provide “palliative care” to Archie would “not be appropriate” without a court order.

A Department of Health and Social Care spokesperson said: “We recognise this is an exceptionally difficult time for Archie Battersbee’s family and our thoughts are with them.

“We have received the letter and will respond in due course.”