Spanish Foreign Minister Josep Borrell said that US President Donald Trump has proposed building a wall along the Sahara border to stop the arrival of migrants from sub-Saharan Africa, as he intends to do with Mexico.

"Closing ports is not a solution, nor is building a wall along the Sahara, as US President Trump has proposed," Borrell said at a meeting this week, according to Spanish media.

The remarks come at a time when European leaders are holding talks in Salzburg, Austria, on how to deal with the migration crisis and refugees.

Spain is at the heart of this crisis after it became the first gateway to immigrants from Africa to Europe by sea and land.

The majority of these migrants cross the desert to reach Morocco and from there to Spain via the Mediterranean on dangerous and sometimes fatal trips.

Trump suggested building a wall along the 3,200 km American-Mexican border, which would cost about $20 billion, according to some estimates.

The Sahara extends across North Africa from the Red Sea eastwards to the Atlantic Ocean to the west, which is about 5,000 km long, and includes Arab countries such as Algeria, Morocco, Mauritania and Libya.