US and Moroccan officials have had talks in Western Sahara on plans to open an American consulate in the disputed territory.
The visit by the US envoy, David Schenker, follows President Trump's controversial decision last month to recognise Morocco's sovereignty over Western Sahara - where the indigenous Sahrawi people want a state of their own.
Mr Trump's move overturned America's longstanding, neutral position on the dispute, and was part of a deal in which Morocco agreed to re-establish relations with Israel.
Saharawi nationalists condemn US-Morocco pact
The US decision to recognise Morocco's claim over the disputed Western Sahara region has angered the territory's Polisario Front, whose spokesman told BBC Focus on Africa it was a "dangerous setback".
"Sovereignty over Western Sahara is a decision that should be taken exclusively by the Saharawi people through a genuine expression of their will," said spokesman Oubi Bouchraya Bachi, adding "it doesn’t belong to the US" or any other power.
Western Sahara was annexed by Morocco in 1975. A 16-year-long insurgency ended with a UN-brokered truce in 1991 and the promise of a referendum on independence, which has yet to take place.
The Polisario Front is a nationalist group backed by Algeria which has been seeking to establish an independent state - a claim recognised by the African Union.
The announcement by outgoing US President Donald Trump comes weeks after hostilities between Moroccan and Polisario forces resumed, breaking almost three decades of ceasefire.
The deal is part of a wider agreement between the US and Morocco that sees it normalise relations with Israel.
"We have been warning that importing the Middle East dynamic to North Africa will engender a lot of instability," Mr Bachi said of the US-Morocco pact.
"We are very hopeful the new administration [in the US] will take a different step," he added.
There has been tension recently in Western Sahara following military manoeuvres in the former demilitarised zone of Guerguerat.
The Polisario Front, which wants independence, says that a 29 year-long ceasefire agreement was broken when Moroccan forces deployed troops and tanks to the UN-patrolled border zone in the disputed territory.
In a statement issued on Tuesday, Polisario said the Moroccan operation was a premeditated attempt to prevent the latest efforts by the UN to discuss their demands.
The Saharawi people, many of whom live in refugee camps in Tindouf in Algeria as well as within Morocco, have long called for a referendum on self-determination.
Lotfi Bouchaara, Morocco's ambassador to Moscow, told the BBC's Focus on Africa programme that Morocco did not breach the ceasefire but its military was responding to a provocation by Polisario fighters who blocked a key road to Mauritania.
Morocco had reacted with "restraint", he said.
"War is always a bad solution... we are ready to engage, we are committed to the political process," he added.
Listen to the full interview:
Western Sahara: Why has fighting returned to north-west Africa?
The Polisario Front says Morocco has broken a 30-year ceasefire, sparking a return to war.
Gunfire continues in Western Sahara buffer zone
Gunfire has continued along the disputed buffer zone
between Morocco and the area held by the pro-independence Polisario Front in
Western Sahara this week.
Stephane Dujarric on Tuesday said the peacekeeping mission in Western Sahara (Minurso) "continues
to receive reports of shots being fired during the night at various locations”.
said its fighters "inflicted human and material losses" in attacks
along the front on Tuesday, but there was no independent confirmation, the AFP
news agency reports.
Sidi Omar, the Polisario’s
ambassador to the UN, said the actions of the
Moroccan forces had reignited a war after 30 years of a ceasefire.
"The situation now is a state of war, both parties are
engaged militarily along the Moroccan military wall and the shelling, firing
continues," he told the BBC NewsDay programme.
The flare-up started last Friday when Moroccan troops
launched an operation to open a highway through the Western Sahara to
A ceasefire agreement between Morocco and the
Polisario Front has lasted since 1991, keeping both sides behind a 2,700 km (1,700 mile) buffer zone sown with an estimated seven million landmines.
Polisario Front condemns Spain over travel warning
BBC World Service
The Polisario Front has condemned the Spanish government's warning to its citizens not to travel to Sahawri refugee camps in Algeria.
The Spanish foreign ministry said the intelligence services had reliable information that an Islamic State group affiliate was planning attacks on Spaniards in the camps around the Algerian city of Tindouf.
The Polisario Front, which is based in the camps, called the warning unfounded, saying several international aid organisations worked there securely.
Polisario is recognised by the UN as the representative of the Saharwi people from the former Spanish colony of Western Sahara, who have never accepted assimilation into Morocco.