Morocco and Western Sahara's Polisario independence movement ended a fourth round of talks near New York City on Tuesday without narrowing differences on Africa's longest-running territorial dispute.

U.N. mediator Peter van Walsum said the sides had agreed to meet again at the same location in the town of Manhasset, New York, for further talks on the rival plans they offered last April on the territory's future.

Polisario's U.N. representative Ahmed Boukhari said there was no substantial progress. "Morocco is insisting that the only solution is their proposal of autonomy," he said.

"We don't believe that the Manhasset process is dead," he said. Boukhari said no date had been set for the next round of talks and "We don't expect something very soon."

Morocco took control of most of Western Sahara in 1975 when colonial power Spain withdrew, prompting a guerrilla war for independence that lasted until 1991 when the United Nations brokered a cease-fire and sent in peacekeepers.

The desert territory of 260,000 on Africa's Atlantic coast holds phosphates, rich fisheries and potentially offshore oil.

Rabat is trying to persuade Polisario to accept its plan for Western Sahara to be an autonomous part of Morocco. Polisario proposes a referendum among ethnic Sahrawis that includes an option of independence.

No state recognizes Morocco's rule over Western Sahara but the Security Council is divided. Some nonaligned states back Polisario, but France and the United States support Morocco.

Boukhari said Morocco had rejected all but one proposal for confidence-building measures such as exchanging political delegations and creating a military commission to enhance a ceasefire. Both sides did agree on expanding family visits.

"The atmosphere, the climate, was not good in terms of tangible tension," Boukhari said, adding that the delegations did not even dine together privately.

Morocco's U.N. mission issued a press statement saying its delegation had shown "good faith" and willingness to engage in serious dialogue but had been met with "rigid and outdated positions from the other parties who didn't show any positive willingness to resolve the Sahara ... issue."

It accused Polisario of provocative acts in the buffer zone and trying to escalate the situation. "One can wonder how we can sustain negotiations" given such behavior, it said, while adding that Morocca remained committed to the negotiations.

Boukhari urged the Security Council to push for a referendum on autonomy or independence. "We need the help, credible help from the Security Council to make sure that we will not see a new failure in U.N. efforts."