The British government says the first flight forcibly taking asylum-seekers to Rwanda as part of a new policy, is scheduled for 14 June.
The Home Office did not specify how many refugees would be removed.
An official told the BBC that all of them were now being held in detention centres.
Priti Patel, the home secretary, said she expected - but would not be deterred by - legal attempts to prevent the removal to Rwanda of people who had entered the UK from France by boat.