Reform UK says it would offer payments to countries like Afghanistan as part of a plan to enable hundreds of thousands of migrant deportations if it won power.
Party leader Nigel Farage set out a five-year plan to detain and deport all migrants who arrive in the UK without permission and suggested 600,000 people could be sent back over five years.
Under the plan, named Operation Restoring Justice, Reform UK would bar anyone who comes to the UK on small boats from claiming asylum, and strike deals with countries to return those people.
Reform UK says it would make £2bn available for returns deals, with aid offered as an incentive and sanctions potentially imposed on uncooperative countries.
Launching his plan, Farage described illegal migration as a "scourge" on the UK.
