Ahmed Bujari, the Polisario's UN representative, said he hoped that "Morocco this time is going to co-operate for the full implementation" of UN resolutions on the issue and "will engage in substantive negotiations".
He told the AFP news agency on Friday that the Moroccans must agree to discuss not just their proposal for broad autonomy for the Western Sahara region but also the Polisario's call for a referendum that would include the option of independence for the former Spanish colony.
Bujari said: "Our people have been frustrated [in their aspiration for independence]. We believe peace is possible... But a new failure of the [negotiation] process would have negative consequences for the entire [northwest African region].
"It could push us on the way to a resumption of hostilities and Morocco will be responsible."
Last October, the UN Security Council voted unanimously to urge the two sides to resume stalled talks "without preconditions" to settle the dispute.
It passed a resolution calling on the parties to "engage in substantive negotiations ... without preconditions and in good faith ... with a view to achieving a just, lasting and mutually acceptable political solution".
Morocco annexed the phosphate-rich, mainly desert Western Sahara in the 1970s following the withdrawal of colonial power Spain, sparking a war with the Polisario's Sahrawi fighters.
1884 - Spain colonises Western Sahara.
1957 - Morocco raises claim to Western Sahara at the UN.
1973 - Polisario formed to wrest Western Sahara from Spanish control and establish an independent Saharan state.
Mid-1975 - Morocco takes territorial dispute to the World Court. Rules that issue should be settled through self-determination.
Late-1975 - Spain withdraws from Western Sahara and Morocco and Mauritania split the territory.
1976 - Polisario relocates to Algeria, proclaims the Saharan Arab Democratic Republic (SADR) with a government-in-exile, launches full-scale war on both Mauritania and Morocco.
1979 - Mauritania signs peace deal with Polisario and withdraws from Western Sahara. Morocco annexes the whole territory.
1984 - SADR is admitted to the Organisation of African Unity. Morocco leaves in protest.
1991 - UN brokers cease-fire between Morocco and Polisario with an agreed referendum for the region.
1992 - Referendum postponed because of dispute over who is eligible to vote.
2003 - UN proposes Western Sahara becomes a semi-autonomous region of Morocco for up to five years, to be followed by a referendum. Polisario endorses the plan but Morocco rejects it.
2007 - Polisario and Moroccan government hold two rounds of UN-backed talks, the first direct negotiations in seven years.
The two sides agreed a ceasefire in 1991, but a promised self-determination referendum never materialised and since 2002, Rabat has insisted that holding such a plebiscite is no longer realistic.
For now, UN peacekeeping forces, known by their French acronym Minurso, maintain the ceasefire agreement.
Speaking hopefully of the talks, Julian Harston, head of the Minurso, told Al Jazeera: "Let them talk in good faith without too much interference from the international community, and see whether they can come up with a solution which is just and which looks after the interests of all the parties involved."
Rabat, however, has been proposing a plan for broader autonomy for the disputed region, envisioning a local government with large powers but within Morocco's sovereignty.
Western Saharan leaders have been discussing the plan as a practical way out of the more than three decades-long conflict, now Africa's longest.
Sid Ezzine Nafaa, a tribal leader in the Western Sahara, told Al Jazeera: "We are for the autonomy plan because it's more suitable for the interest of our region.
"But we want it to be implemented right now so that those who are on the other side of the border can feel its benefits. At the end of the day, they are our children, they are our family.
Despite support from Sahrawis inside Morocco's borders, a breakthrough at the talks looks unlikely.
Hashem Ahelbarra, Al Jazeera's correspondent reporting from Western Sahara, said: "The huge gap in the positions of the concerned parties doesn’t seem to allow for a compromise.
"Moroccans say they have submitted the best plan. The Polisario on the other hand, believes a referendum is the only credible option."