A frozen conflict between Morocco—America's oldest official diplomatic ally—and the separatist Polisario Front is threatening to deteriorate into wider violence.
Improved trade links and an inside track on the Western Sahara issue are among the benefits.
The North African country left the bloc in 1983 due to a row over Western Sahara.
Ban Ki-moon sparked a row with Morocco by describing the disputed territory as under "occupation."
Morocco and Ban Ki-moon's dispute is the most serious since the 1991 ceasefire in Western Sahara.
Morocco has pulled its personnel from a U.N. mission in the disputed region.
Ban Ki-moon recently referred to Morocco's presence in Western Sahara as "occupation."
Ban Ki-moon has described the conflict as a "forgotten humanitarian tragedy."