Western Sahara guerrillas on Thursday released their last Moroccan prisoners, 404 soldiers held for up to 20 years from a war that ended in 1991, the Red Cross announced.

The Moroccans had been held in Polisario Front camps in southern Algeria and were repatriated under Red Cross auspices. Their release after mediation by the United States removes one of the obstacles to peace for the Western Sahara region.

"We absolutely do welcome this, the end of this long period of internment," a Red Cross spokeswoman, Nada Doumani, said.

The soldiers were flown to the Moroccan city of Agadir in planes chartered from the U.S. military.

Sen. Richard Lugar (R-Ind.), chairman of the Senate Foreign Relations Committee, oversaw the handover.

The White House said the release was the result of quiet and intense diplomatic efforts involving the two North African countries and the United States. It said the International Committee of the Red Cross also played a role.

After Morocco annexed Western Sahara, a vast mineral-rich territory once colonized by Spain, Polisario Front rebels based in camps in southern Algeria waged a desert war to gain the territory's independence. The fighting, which pitted 15,000 Polisario guerrillas against Morocco's U.S.-equipped army, ended in 1991 with a U.N.-negotiated cease-fire that called for a referendum on the region's future.

The Polisario Front said it hoped Thursday's release would help clear the way for a peace settlement. It urged Morocco to reciprocate by also releasing prisoners of war and to account for people missing as a result of the conflict.

Some of the last Moroccan prisoners of war arrive at the airport in Agadir, Morocco, after U.S. diplomatic efforts helped secure their freedom.