Morocco will clear the main road linking Western Sahara to Mauritania that has been blocked since October 21 by supporters of the Polisario independence movement, it said on Friday.
The Guerguerat crossing is the main land connection between Morocco and West Africa.
Morocco's army said it had erected a security cordon early on Friday and would carry out an operation to restore traffic.
It said it would use arms only for "legitimate defense."
A senior Foreign Ministry source said Morocco would set up sand barriers to protect the road.
Polisario had previously threatened to respond if any Morocco military or civilian personnel enters the Guerguerat area, warning it could "put an end to the ceasefire and trigger a new war."
On Friday, Polisario said that Morocco has broken the 1991 ceasefire between them and had "begun the battle and ignited the war".
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Pro-Polisario protesters have for weeks blocked the road where it passes through a UN-monitored buffer zone near the Mauritanian border after a UN Security Council resolution that included language seen as favorable to Morocco.
In a statement the Foreign Ministry said Morocco "had no other choice but to assume its responsibilities in order to put an end to the blockade ... and restore the free flow of civilian and commercial traffic."
Morocco took over the desert territory in 1975 when Spanish rule there ended and considers the phosphate-rich region part of its own country.
The Algeria-backed Polisario movement seeks independence for Western Sahara.
Last month the UN Security Council passed resolution 2548 which called for a "realistic, practicable and enduring solution... based on compromise."
That language was widely seen as calling into doubt any referendum on the territory's future – a goal long sought by the Polisario and backed by the United Nations in 1991.