The small Central American nation of Belize has signed an agreement with Washington to act as a 'safe third country' for migrants as they seek asylum in the United States.

Belize PM John Antonio Briceño said the deal - which must be approved by the Belize Senate - will mean that migrants deported from the US could apply for asylum instead of returning to their home countries.

The US State Department called it 'an important milestone in ending illegal immigration', and 'shutting down abuse' of the US asylum system.

The deal appears to be similar to one with Paraguay announced in August.

This year Panama, Costa Rica, El Salvador and Honduras have also taken in people deported by the US.

Human rights groups in the US and abroad have strongly criticised such deals, saying migrants face the risk of being sent to countries where they could be harmed.

Belize's ministry of foreign affairs posted on social media that the agreement 'includes strict security measures to protect Belize's national security and sovereignty'.

Prime Minister Briceño told local media that for Belize it will be 'more like a job programme, whereby people with certain qualifications can come to Belize' and 'participate meaningfully in our economy.'

However, opposition leader Tracy Taegar Panton expressed 'grave concern' about the deal, warning it could disrupt Belize's immigration and asylum systems and impose new burdens on taxpayers.

The US State Department stated that the agreement was 'an important milestone in ending illegal immigration, shutting down abuse of our nation's asylum system, and reinforcing our shared commitment to tackling challenges in our hemisphere together'.

Further details of the agreement have not yet been released, but as the U.S. continues its efforts to remove undocumented migrants, this agreement marks a significant step in the evolving landscape of immigration policy.