Amnesty International Sunday urged Algeria to adopt a law on the right to asylum and to open an investigation into the deportation of sub-Saharan migrants from the country this month.

"The authorities should decriminalise irregular immigration, adopt a law on (the right to) asylum and fight racism against sub-Saharans in the country," the group's Algeria office said in a statement in French.

A draft law on the right to asylum has been in the works for five years, Amnesty said.

The statement comes after Algeria on Saturday defended its treatment of a group of around 260 Malian migrants rounded up and deported to their country at the start of December, dismissing charges of brutality.

Amnesty called on Algiers "to open up a prompt and impartial inquiry into the cases of arbitrary expulsions and allegations of mistreatment".

Algerian law criminalises irregular migration into the country and stipulates jail time for anyone who aids a migrant who entered Algeria illegally.

This means migrants are "extremely vulnerable" and "prevents them from reporting abuse for fear of being pursued, jailed or deported", Amnesty said.

Algeria has expelled thousands of African migrants since the descent into chaos over the past five years of Libya, a focal point for migrants trying to cross the Mediterranean to Europe.

The migrants are generally arrested in cities of northern Algeria bordering the sea and bused to a reception centre in the south before being deported.