The Polisario Front on Monday vowed to end a decades-old ceasefire deal with Morocco after it accused Rabat of moving its forces to an area manned by UN peacekeepers.
"Moroccan occupying forces began last night to move a large number of gendarmes and other security forces in the region," said a statement received by AFP.
"This will also mean the end of the ceasefire agreement and will start a new war throughout the region," the statement added.
The area at the center of new tensions is known as Guerguerat, a small village meant to act as a buffer zone between Western Sahara and Moroccan territory.
The group promised a 'vigorous response' to the 'blatant aggression' in the statement.
The Polisario movement fought a guerilla war against Moroccan control of Western Sahara, before a UN-brokered ceasefire in 1991. Morocco maintains that the territory is an integral part of the kingdom and has dismissed calls for independence.
Despite better ties with the African Union, many countries still see Morocco as a colonial power in Western Sahara.
The kingdom has proposed greater autonomy for the mostly desert region, but Polisario has insisted on the right of the Sahrawi people to statehood.