Human rights campaigners say they will "see the government in court" after the Home Office published its highly anticipated safety assessment on Rwanda - where it plans to send asylum seekers.
The report outlines official country guidance and admits LGBTQI+ migrants could be "at risk of discrimination".
Detention Action, which is part of a number of organisations paving the way for legal action against the government, says it is concerned that the document indicates anyone seeking asylum is at risk of being sent to Rwanda with the exception of unaccompanied children.
This would include people who have been trafficked; those who say they have mental health problems; families with children and those who identify as LGBTQI+.
It was previously believed families with children would be exempt.
The guidance will help Home Office workers decide whether an asylum seeker whose claim to stay in the UK has been ruled as inadmissible is suitable for relocation to Rwanda.
It says there is a "functioning asylum process in operation in Rwanda" and insists it has a "positive, welcoming attitude to refugees".
Bella Sankey, director of Detention Action, said: "People are already being harmed, living in fear of receiving these letters, including asylum-seeking families with children. We'll continue this fight to protect people's rights in court."
On the issue of the treatment by Rwanda of LGBTQI+ applicants, the report says: "Despite some evidence of discrimination and intolerance towards persons based on their sexual orientation and gender identity or expression, in general the treatment is not sufficiently serious by its nature and/or repetition to establish a systemic risk or to amount to persecution or serious harm."
But it admits: "Rwanda is a largely Christian conservative society and the topic of same-sex sexual relationships is considered taboo."
It also says the policy will have a "greater impact on those of Muslim faith" because "individuals making a clandestine journey to the UK are more likely to be of Muslim faith compared to other routes".
The assessment says there "are not substantial grounds" for believing that a woman or girl, if relocated, would face a real risk of being subjected to treatment that is likely to be contrary to the European Convention on Human Rights.
With regard to concerns over the amount of time asylum seekers will spend in Rwanda waiting for a decision on their case, the report says the government of Rwanda has acknowledged that it is "not always possible to meet all these timeframes in practice".
The assessment says any person relocated from the UK would not be required to live in a refugee camp and will not have the right to work while their claim is pending.
Lewis Mudge, Central Africa director at Human Rights Watch, said: "This report is not grounded in reality. The Rwandan government has an abysmal record when it comes to guaranteeing internationally recognised refugee rights, statutes and protocols. It's difficult to imagine a less genuine assessment of Rwanda's shocking human rights record."
Confirming that the first letters will be sent to asylum seekers this week telling them they could be sent to Rwanda, Home Secretary Priti Patel said: '"This is just the first stage of the process and we know it will take time as some will seek to frustrate the process and delay removals.
"I will not be deterred from acting to deliver on the changes the British people voted for to take back control of our money, laws and borders."