Eamon Courtenay said on Twitter that Belize was not in negotiations with Britain to become an offshore processing site for asylum seekers.
British authorities plan to send asylum seekers to Rwanda, but the scheme has faced legal challenges.
Reports suggest UK Home Secretary Suella Braverman is considering alternative destinations, including Paraguay, Peru and Belize.
Mr Courtney said Belize was not in negotiations with the UK "or any other country" to accept asylum seekers.
"We will not agree to accept exported migrants. That is inhumane and contrary to international law," he said.
Belize, in Central America, gained independence from the UK in 1981, but remains a member of the Commonwealth.
Mr Courtney’s criticism of the policy comes after Albanian Prime Minister Edi Rama accused Britain of becoming a “madhouse” during a migration crisis caused by “failed policies”.
Britain on Thursday also sought to defuse a row with Tirana after Prime Minister Edi Rama accused it of blaming Albanians for causing its immigration problems.
Foreign Secretary James Cleverly held talks with Mr Rama in London and tweeted late Wednesday that they had "an important meeting".
"We agree that we must break the business model of people smugglers who are putting lives at risk," he added.
In April, Priti Patel, UK home secretary at the time, signed what she described as a “world-first agreement” to deport some asylum seekers to Rwanda.
As part of the deal, the UK paid Rwanda £120 million ($134.7m), but the first scheduled deportation in June was grounded after several legal challenges were brought against the government.
In September, a five-day judicial was held to assesses the lawfulness of the policy.
Ms Braverman has now pushed for talks to expand the policy to countries in Central and South America, with another African country “also in the mix”, The Daily Express reported.
She is under mounting pressure to tackle the migrant crisis as the government faces legal action over an asylum centre in southern England condemned by senior MPs.
On Tuesday, asylum seekers from a processing centre in Manston were left at London’s Victoria Coach Station without accommodation.
They were among hundreds thought to have been moved from the Manston site, a disused airfield, amid concerns it was dangerously overcrowded.
The number of migrants who have used small boats to cross the Channel to the UK this year is approaching 40,000.