The first international treaty on managing migration is to be signed at a two-day gathering in Morocco.

The UN's Global Compact for Migration sets out a number of objectives, including the integrated management of borders and ensuring that migrants have access to basic services.

German Chancellor Angela Merkel is among the leaders expected to attend the meeting in Marrakesh.

But a large number of countries, from Poland to Australia, have refused to take part.

A BBC correspondent says political parties in many parts of the world are in no mood to sign up to multilateral solutions to problems that cross borders.