WASHINGTON — Morocco has canceled its annual military exercises with the United States after the Obama administration supported adding human-rights monitoring to the U.N. mission to the disputed Western Sahara territory, U.S. officials said.

The 13th annual "African Lion" exercise — involving 1,400 U.S. servicemen and 900 Moroccan troops — had been set to start Wednesday with many personnel already in place and international observers invited.

The U.S. officials spoke on condition of anonymity because there has not yet been a formal announcement of the cancellation. Morocco's government spokesman declined to comment.

Mustapha Khalfi, the spokesman who doubles as the minister of communication, did summon journalists Tuesday to express his government's anger over initiatives to broaden the U.N. mission's mandate to include human-rights monitoring.

"It is an attack on the national sovereignty of Morocco and will have negative consequences on the stability of the whole region," he warned. "We count on the wisdom of the members of the Security Council to avoid such initiatives."

Morocco annexed the former Spanish colony of Western Sahara in 1976, sparking a decades-long battle for independence by the Polisario Front group, which ended with a U.N.-brokered 1991 cease-fire.

Ownership of the mineral-rich region, however, is an incredibly sensitive matter for the Moroccans and their highest foreign priority. Morocco has proposed a wide autonomy for Western Sahara, but the Polisario insist on the "inalienable right" to self-determination through a referendum. Neither side has budged and sporadic talks have ended in a stalemate.

The U.N. observer mission in the Western Sahara currently has 183 military observers, 26 troops and six civilian police.