RABAT (Reuters) - Morocco has applied to rejoin the African Union 32 years after it left, the bloc said on Friday, as the North African kingdom seeks support for its plan to end a decades-old row over Western Sahara.

Morocco, which claims the sparsely populated stretch of desert, left the African Union in 1984 when the bloc recognized a republic covering part of the territory declared by Polisario Front independence fighters.

Morocco submitted its letter of intention to rejoin the union on Thursday, the AU said in a statement, without giving details of any reasons.

But Morocco has stepped up lobbying efforts across the continent its bid to offer Western Sahara autonomy under Moroccan sovereignty. Moroccan officials have recently made visits to Algiers, Abuja and Nairobi.

Rabat says at least 36 of the 54 AU member states do not acknowledge the Polisario Front's breakaway territory, and wants the bloc to withdraw support.

Morocco has controlled most of the territory, which is rich in phosphates and has seen some initial oil exploration efforts, since 1975. A ceasefire in 1991 called for a referendum on self-determination for Western Sahara, but the vote has never taken place.

Tensions have been rising between Morocco and Polisario after a standoff between their forces in a U.N.-mandated buffer zone near the Mauritania frontier in the Guerguerat area. U.N. peacekeepers have intervened between the Moroccan gendarmerie and a Polisario brigade in the area.

(Reporting by Aziz El Yaakoubi; Writing by Patrick Markey; Editing by Andrew Heavens)