Ejecting Western Sahara from the African Union is "impossible", Algeria's prime minister said Thursday after his country's arch-rival Morocco urged the bloc to rethink its position on the "phantom state".

Morocco quit the AU in protest in 1984 after the Sahrawi Arab Democratic Republic (SADR) was accepted as a member, but its monarch said Sunday that it hopes to rejoin the bloc.

Morocco regards the former Spanish colony as its sovereign territory, but a local independence movement -- backed by Algeria -- has long fought for self-determination.

On Sunday Morocco's King Mohammed VI told AU leaders his country wants to rejoin the union, but said recognition of a "pseudo state" is "hard for the Moroccan people to accept".

Algerian Prime Minister Abdelmalek Sellal told journalists outside parliament on Thursday that reconsidering Western Sahara's status was "impossible".

"If Morocco wants to join the AU without preconditions, Algeria will have no problem, but there are procedures to follow," he said.

Morocco's return to the AU would need to be validated by a vote.

In 1991, the United Nations brokered a ceasefire between Moroccan troops and Sahrawi rebels of the Algerian-backed independence movement the Polisario Front but a promised referendum to settle the status of the desert territory has yet to materialise.

"The position of Algeria is clear and constant: we support the UN solution and respect for international law," said Sellal.

Algeria has "no problem with the Moroccan people or Morocco in general," he said.

He said Algeria was ready to re-open discussions on bilateral cooperation. Algeria has kept the land border between the two countries closed since 1994.

In a message sent to an AU summit in Kigali and quoted by the MAP Moroccan news agency, King Mohammed VI said that although Morocco had left the club, "it never quit Africa".

"For a long time our friends have been asking us to return to them, so that Morocco can take up its natural place within its institutional family. The moment has now come," the monarch said on Sunday.